Test PG counters is accurate when using create_only_config_db_buffers…

[arfeigin]

… optimization

Description of PR

This test is checking that PG counters inside snmp docker are accurate when using create_only_config_db_counters optimization.

Summary:
Fixes sonic-net/sonic-buildimage#17448 and is related to the fix, available in sonic-net/sonic-snmpagent#303

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• Test case(new/improvement)

Back port request

• 201911
• 202012
• 202205
• 202305
• 202311

Approach

What is the motivation for this PR?

To enhance the bug fix mentioned above solving an issue with PG counters optimization.

How did you do it?

  - Set "create_only_config_db_buffers" to true in config db, to create only relevant PG counters.
  - Remove one of the buffer queues, Ethernet0|3-4 is arbitrary chosen.
  - Using snmpwalk compare number of PG counters on Ethernet0, assuming there will be 8 less after
    removing the buffer. (Assuming unicast only, 4 pg counters for each lane in this case).

How did you verify/test it?

Run the test multiple times on various setups.

Any platform specific information?

Test assumes unicast only

Supported testbed topology if it's a new test case?

Documentation