Generate switch level dscp_to_tc_map entry from qos_config template

[bingwang-ms]

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

Why I did it

This PR is to update template for generating switch level DSCP_TO_TC_MAP config.
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 is generated from qos_config.j2.

Related PRs

Repo	PR title	State
sonic-swss	Apply DSCP_TO_TC_MAP from PORT_QOS_MAP|global to switch level
sonic-utilities	Update db_migrator to support PORT_QOS_MAP|global
sonic-buildimage	Update YANG for PORT_QOS_MAP to support switch level mapping

How I did it

Update the template qos_config.j2.

How to verify it

Verified by vstest.

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

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

Description for the changelog

This PR is to update template for generating switch level DSCP_TO_TC_MAP config.

Link to config_db schema for YANG module changes

TODO

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

[prsunny]

lgtm

[bingwang-ms]

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