Added route reflector scale test (#3812)

* Added route reflector scale test

* added oc paths and rpcs

* fixed generated prefixes

* go formatted

feature/bgp/routereflector/otg_tests/route_reflector_scale/README.md

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+# RT-1.8: BGP Route Reflector Test at scale
+
+## Summary
+
+*   BGP route reflector capabilities check
+*   Ensure functionality of different OC paths for "supported-capabilities",
+    "BGP peer-type", "BGP Neighbor details" and "BGP transport session
+    parameters"
+
+## Topology
+
+ATE (Port1) <-EBGP-> (Port1) DUT (Port2) <-IS-IS/IBGP-> (Port2) ATE, DUT (Port3)
+<-IS-IS/IBGP-> (Port3) ATE
+
+*   Connect ATE Port1 to DUT port1 (EBGP peering)
+*   Connect ATE Port2 to DUT port2 (For IS-IS adjacency and IBGP peer
+    reachability)
+*   Connect ATE Port3 to DUT port3 (For IS-IS adjacency and IBGP peer
+    reachability)
+
+## Test Procedure
+
+*   Establish IS-IS adjacency between ATE Port2 <-> DUT Port2, ATE Port3 <-> DUT
+    Port3.
+*   Establish BGP sessions as follows between ATE and DUT.
+  *   ATE port2 and ATE port3 are emulating RR clients peered with the DUT
+      acting as the RR server. DUT's loopback address should be used for the
+      IBGP peering and "transport/config/local-address" OC path should be used
+      on DUT to configure BGP transport address for IBGP peering. ATE
+      addresses used for the IBGP peering (different from ATE Port1 and ATE
+      Port2 addreses) and DUT loopback addresses should be reachable via
+      IS-IS. Each of the ATEs should advertise 5M IPv4 and 2M IPv6 prefixes to
+      the RR over the IBGP peering, with different path attributes like
+      protocol next-hops, local-preference, community and MED. Among these, 2M
+      v4 and 1M v6 prefixes are unique. Among the 2M IPv4 prefixes as well,
+      1.5M are non RFC1918 or RFC6598 addresses and represent Internet
+      prefixes. Similarly, 600k IPv6 prefixes will represent internet
+      prefixes. These prefixes should be common between the 2xATEs with
+      different path-attributes for protocol next-hop, AS-Path and community.
+      Balance 500k IPv4 and 400k IPv6 prefixes represent internal subnets and
+      should include some prefixes that are unique to each of the ATEs.
+      Remaining prefixes(3M IPv4 and 1M IPv6) in the mix need to be common
+      between the 2xATEs and should have identical path attributes except for
+      the protocol next-hops.
+  *   The DUT Port1 has eBGP peering with ATE Port 1 and is receiving 10M IPv4
+      and 3M IPv6 Internet routes with different path attributes like protocol
+      next-hops, AS-Path, Origin, MED and communities. Out of these, only 1.5M
+      IPv4 and 600k IPv6 prefixes are unique and will be programmed to the
+      FIB.
+    *   The 1.5M IPv4 and 600k IPv6 unique prefixes representing internet
+        addresses should be the same as the ones learnt by the DUT over the
+        IBGP peering but with different path attributes like protocol
+        Next-hops, communities etc.
+    *   The DUT should automatically determine the BGP transport source
+        address based on the nearest interface. Hence, the OC path
+        "transport/config/local-address" shouldn't be used.
+    *   The DUT should advertise these EBGP learnt prefixes over the 2xIBGP
+        peering. [*] Expectations are that the DUT will prefer EBGP learnt
+        internet routes over the IBGP learnt routes. For the IBGP learnt
+        internal prefixes, the DUT should advertise the same over the EBGP
+        peering. [**] Expectations are that the DUT would advertise all
+        internal IPv4 and IPv6 prefixes to the EBGP peers.
+  *   Validate session state on ATE ports and DUT using telemetry.
+    *   The check should also include accurately receiving values for the
+        path "transport/state/local-address" for RRCs as well as for the
+        EBGP peering.
+    *   Validate accuracy of the peer-type leaf (neighbor/config/peer-type)
+        for EBGP and IBGP peering.
+  *   Validate session state and capabilities received on DUT using telemetry.
+    *   For capabilities, just make sure that the length of the list
+        "neighbor/state/supported-capabilities" is non-zero
+  *   Validate route receipt.
+    *   Ensure that the DUT advertises all the IBGP learnt routes to the
+        EBGP peer. Pass expectation covered in context in [**] above
+    *   Ensure that the DUT advertises all the EBGP learnt routes to the
+        IBGP peers. Pass expectation covered in context in [*] above
+    *   Ensure that the DUT as RR server advertises routes learnt from each
+        of the RRC to the other.
+  *   Validate BGP route/path attributes below for each of the EBGP and IBGP
+      learnt routes
+    *   Next-Hop
+    *   Local Pref
+    *   Communities
+    *   AS-Path
+
+## OpenConfig Path and RPC Coverage
+
+```yaml
+paths:
+  /network-instances/network-instance/protocols/protocol/bgp/neighbors/neighbor/route-reflector/config/route-reflector-cluster-id:
+  /network-instances/network-instance/protocols/protocol/bgp/neighbors/neighbor/route-reflector/config/route-reflector-client:
+  /network-instances/network-instance/protocols/protocol/bgp/neighbors/neighbor/config/peer-type:
+  /network-instances/network-instance/protocols/protocol/bgp/neighbors/neighbor/transport/config/local-address:
+  /network-instances/network-instance/protocols/protocol/bgp/neighbors/neighbor/route-reflector/state/route-reflector-cluster-id:
+  /network-instances/network-instance/protocols/protocol/bgp/neighbors/neighbor/route-reflector/state/route-reflector-client:
+  /network-instances/network-instance/protocols/protocol/bgp/neighbors/neighbor/state/peer-type:
+  /network-instances/network-instance/protocols/protocol/bgp/neighbors/neighbor/state/supported-capabilities:
+
+rpcs:
+  gnmi:
+    gNMI.Get:
+    gNMI.Subscribe:
+    gNMI.Set:
+```

feature/bgp/routereflector/otg_tests/route_reflector_scale/metadata.textproto

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+# proto-file: github.com/openconfig/featureprofiles/proto/metadata.proto
+# proto-message: Metadata
+
+uuid: "832df980-9bb9-41d2-9767-e592e193f876"
+plan_id: "RT-1.8"
+description: "BGP Route Reflector Test at scale"
+testbed: TESTBED_DUT_ATE_4LINKS
+platform_exceptions: {
+  platform: {
+    vendor: ARISTA
+  }
+  deviations: {
+    omit_l2_mtu: true
+    interface_enabled: true
+    default_network_instance: "default"
+    missing_isis_interface_afi_safi_enable: true
+    isis_interface_afi_unsupported: true
+    isis_instance_enabled_required: true
+    bgp_default_policy_unsupported: true
+    isis_require_same_l1_metric_with_l2_metric: true
+  }
+}