[watermarks] add watermarkstat, watermarkcfg and aliases

[mykolaf]

- What I did
Add Cli and scripts for Watermark feature
High Level Design Document
- How I did it
Added 2 scripts:

• watermarkstat
• watermarkcfg

Extended show, clear and config CLI groups.

- How to verify it

- Previous command output (if the output of a command-line utility has changed)

- New command output (if the output of a command-line utility has changed)

~$ show priority-group watermark shared
Ingress shared pool occupancy per PG:
       Port    PG0    PG1    PG2    PG3    PG4    PG5    PG6    PG7
-----------  -----  -----  -----  -----  -----  -----  -----  -----
  Ethernet0     96      0      0      0      0      0      0      0
  Ethernet4     96      0      0      0      0      0      0      0
  Ethernet8     96      0      0      0      0      0      0      0
 Ethernet12     96      0      0      0      0      0      0      0
 Ethernet16     96      0      0      0      0      0      0      0
 Ethernet20     96      0      0      0      0      0      0      0
 Ethernet24   9120      0      0      0      0      0      0      0
 Ethernet28     96      0      0      0      0      0      0      0
 Ethernet32     96      0      0      0      0      0      0      0

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