[exporter][pulsar][doc] Add pulsarexporter README.md (#12108)

* add pulsarexporter README.md

* add README.md header & unreleased yaml file

* add README.md header & unreleased yaml file

* add [in-development] link

exporter/pulsarexporter/README.md

@@ -0,0 +1,74 @@
+# Pulsar Exporter
+
+| Status                   |                       |
+| ------------------------ |-----------------------|
+| Stability                | [in-development]      |
+| Supported pipeline types | traces, logs, metrics |
+| Distributions            | none                  |
+
+Pulsar exporter exports logs, metrics, and traces to Pulsar. This exporter uses a synchronous producer
+that blocks and able to batch messages.
+
+Supported pipeline types: logs, metrics, traces
+
+## Get Started
+
+The following settings can be optionally configured:
+- `endpoint` (default = pulsar://localhost:6650): The url of pulsar cluster.
+- `topic` (default = otlp_spans for traces, otlp_metrics for metrics, otlp_logs for logs): The name of the pulsar topic to export to.
+- `encoding` (default = otlp_proto): The encoding of the traces sent to pulsar. All available encodings:
+    - `otlp_proto`: payload is Protobuf serialized from `ExportTraceServiceRequest` if set as a traces exporter or `ExportMetricsServiceRequest` for metrics or `ExportLogsServiceRequest` for logs.
+    - `otlp_json`:  ** EXPERIMENTAL ** payload is JSON serialized from `ExportTraceServiceRequest` if set as a traces exporter or `ExportMetricsServiceRequest` for metrics or `ExportLogsServiceRequest` for logs.
+    - The following encodings are valid *only* for **traces**.
+        - `jaeger_proto`: the payload is serialized to a single Jaeger proto `Span`, and keyed by TraceID.
+        - `jaeger_json`: the payload is serialized to a single Jaeger JSON Span using `jsonpb`, and keyed by TraceID.
+- `auth`
+    - `tls`
+        - `cert_file`:
+        - `key_file`:
+    - `token`
+        - `token`
+    - `oauth2`
+        - `issuer_url`:
+        - `client_id`:
+        - `audience`:
+    - `athenz`
+        - `provider_domain`:
+        - `tenant_domain`:
+        - `tenant_service`:
+        - `private_key`:
+        - `key_id`:
+        - `principal_header`:
+        - `zts_url`:
+- `tls_trust_certs_file_path`: path to the CA cert. For a client this verifies the server certificate. Should
+  only be used if `insecure` is set to true.
+- `tls_allow_insecure_connection`: configure whether the Pulsar client accept untrusted TLS certificate from broker (default: false)
+- `retry_on_failure`
+    - `enabled` (default = true)
+    - `initial_interval` (default = 5s): Time to wait after the first failure before retrying; ignored if `enabled` is `false`
+    - `max_interval` (default = 30s): Is the upper bound on backoff; ignored if `enabled` is `false`
+    - `max_elapsed_time` (default = 120s): Is the maximum amount of time spent trying to send a batch; ignored if `enabled` is `false`
+- `sending_queue`
+    - `enabled` (default = true)
+    - `num_consumers` (default = 10): Number of consumers that dequeue batches; ignored if `enabled` is `false`
+    - `queue_size` (default = 5000): Maximum number of batches kept in memory before dropping data; ignored if `enabled` is `false`;
+      User should calculate this as `num_seconds * requests_per_second` where:
+        - `num_seconds` is the number of seconds to buffer in case of a backend outage
+        - `requests_per_second` is the average number of requests per seconds.
+
+Example configuration:
+```yaml
+exporters:
+  pulsar:
+    service_url: pulsar://localhost:6650
+    topic: otlp-spans
+    encoding: otlp_proto
+    auth:
+      tls:
+        cert_file: cert.pem
+        key_file: key.pem
+    tls_allow_insecure_connection: false
+    tls_trust_certs_file_path: ca.pem
+```
+
+[in-development]:https://github.com/open-telemetry/opentelemetry-collector#in-development

unreleased/pulsar_exporter_doc.yaml

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+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: new_component
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: pulsarexporter
+
+# A brief description of the change
+note: Add Apache Pulsar exporter doc
+
+# One or more tracking issues related to the change
+issues: [ 9795 ]