Test polling only configured buffer queue counters (#11941)

## Description of PR
This test is checking that buffer queue counters inside snmp docker are inline when using create_only_config_db_counters optimization.

Summary:
Accompanies "Fix SNMP dropping some of the queue counter when create_only_config_db_buffers is set to true" (sonic-net/sonic-snmpagent#303) which fixes the issue: "The feature "polling only configured ports buffer queue" will break SNMP" (sonic-net/sonic-buildimage#17448).

### Type of change

- [ ] Bug fix
- [ ] Testbed and Framework(new/improvement)
- [x] Test case(new/improvement)

## Approach
#### What is the motivation for this PR?
To enhance the bug fix mentioned above, solving an issue with buffer queue counters optimization.
#### How did you do it?
- Set "create_only_config_db_buffers" to true in config db, to create only relevant counters
- Remove one of the buffer queues, Ethernet0|3-4 is chosen arbitrary
- Using snmpwalk compare number of queue counters on Ethernet0, assuming there will be 8 less after removing the buffer. (Assuming unicast only, 4 counters for each queue in this case)
#### How did you verify/test it?
Run the test multiple times on various setups.
Run the test while reverting the fix mentioned above to see the different result.
### Supported testbed topology if it's a new test case?
Any

tests/snmp/test_snmp_queue_counters.py

@@ -0,0 +1,87 @@
+import pytest
+import json
+from tests.common import config_reload
+from tests.common.helpers.assertions import pytest_assert
+
+CFG_DB_PATH = "/etc/sonic/config_db.json"
+ORIG_CFG_DB = "/etc/sonic/orig_config_db.json"
+UNICAST_CTRS = 4
+MULTICAST_CTRS = 4
+BUFFER_QUEUES_REMOVED = 2
+
+pytestmark = [
+    pytest.mark.topology('any'),
+    pytest.mark.device_type('vs')
+]
+
+
+def load_new_cfg(duthost, data):
+    duthost.copy(content=json.dumps(data, indent=4), dest=CFG_DB_PATH)
+    config_reload(duthost, config_source='config_db', safe_reload=True)
+
+
+def get_queue_ctrs(duthost, cmd):
+    return len(duthost.shell(cmd)["stdout_lines"])
+
+
+def test_snmp_queue_counters(duthosts,
+                             enum_rand_one_per_hwsku_frontend_hostname,
+                             creds_all_duts):
+    """
+    Test SNMP queue counters
+      - Set "create_only_config_db_buffers" to true in config db, to create
+      only relevant counters
+      - Remove one of the buffer queues, Ethernet0|3-4 is chosen arbitrary
+      - Using snmpwalk compare number of queue counters on Ethernet0, assuming
+      there will be 8 less after removing the buffer. (Assuming unicast only,
+      4 counters for each queue in this case)
+    This test covers the issue: 'The feature "polling only configured ports
+    buffer queue" will break SNMP'
+    https://github.com/sonic-net/sonic-buildimage/issues/17448
+    """
+
+    duthost = duthosts[enum_rand_one_per_hwsku_frontend_hostname]
+    hostip = duthost.host.options['inventory_manager'].get_host(
+        duthost.hostname).vars['ansible_host']
+    Ethernet0_queue_cntrs_oid = '1.3.6.1.4.1.9.9.580.1.5.5.1.4.1'
+    get_bfr_queue_cntrs_cmd \
+        = "docker exec snmp snmpwalk -v2c -c {} {} {}".format(
+            creds_all_duts[duthost.hostname]['snmp_rocommunity'], hostip,
+            Ethernet0_queue_cntrs_oid)
+
+    duthost.shell("sonic-cfggen -d --print-data > {}".format(ORIG_CFG_DB))
+    data = json.loads(duthost.shell("cat {}".format(ORIG_CFG_DB),
+                                    verbose=False)['stdout'])
+
+    # Add create_only_config_db_buffers entry to device metadata to enable
+    # counters optimization and get number of queue counters of Ethernet0 prior
+    # to removing buffer queues
+    data['DEVICE_METADATA']["localhost"]["create_only_config_db_buffers"] \
+        = "true"
+    load_new_cfg(duthost, data)
+    queue_counters_cnt_pre = get_queue_ctrs(duthost, get_bfr_queue_cntrs_cmd)
+
+    # Remove buffer queue and reload and get number of queue counters of
+    # Ethernet0 after removing two buffer queues
+    del data['BUFFER_QUEUE']["Ethernet0|3-4"]
+    load_new_cfg(duthost, data)
+    queue_counters_cnt_post = get_queue_ctrs(duthost, get_bfr_queue_cntrs_cmd)
+
+    unicast_expected_diff = BUFFER_QUEUES_REMOVED * UNICAST_CTRS
+    multicast_expected_diff = unicast_expected_diff + (BUFFER_QUEUES_REMOVED
+                                                       * MULTICAST_CTRS)
+    pytest_assert((queue_counters_cnt_pre - queue_counters_cnt_post)
+                  in [unicast_expected_diff, multicast_expected_diff],
+                  "Queue counters count differs from expected")
+
+
+@pytest.fixture(scope="module")
+def teardown(duthost):
+    """
+    Teardown procedure for all test function
+    :param duthost: DUT host object
+    """
+    yield
+    # Cleanup
+    duthost.copy(src=ORIG_CFG_DB, dest=CFG_DB_PATH)
+    config_reload(duthost, config_source='config_db', safe_reload=True)