[Yang] Update YANG for PORT_QOS_MAP to support switch level mapping

[bingwang-ms]

Signed-off-by: bingwang wang.bing@microsoft.com

Why I did it

This PR is to update Yang model for PORT_QOS_MAP to support switch level mapping.
After PR #10565, there will be two DSCP_TO_TC_MAP

• DSCP_TO_TC_MAP|AZURE is the default map, which is used at port level and switch level
• DSCP_TO_TC_MAP|AZURE_TUNNEL is used to remap the priority of tunnel traffic in dualtor deployment

To address the issue, an entry PORT_QOS_MAP|global will be added into config_db

"PORT_QOS_MAP": {
        "global": {
            "dscp_to_tc_map": "AZURE"
        }
}

The entry will be consumed by qosorch, and the specified map will be applied to switch.

How I did it

Update sonic-port-qos-map.yang

How to verify it

Verified by new test cases

collected 3 items                                                                                                                                                                                     

tests/test_sonic_yang_models.py ..                                                                                                                                                              [ 66%]
tests/yang_model_tests/test_yang_model.py .                                                                                                                                                     [100%]

====================================================================================== 3 passed in 2.48 seconds =======================================================================================

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106
• 202111

Description for the changelog

Update YANG for PORT_QOS_MAP to support switch level mapping.

Link to config_db schema for YANG module changes

To be added.

A picture of a cute animal (not mandatory but encouraged)

[bingwang-ms]

/azp run Azure.sonic-buildimage

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