Add DSCP remap QOS Test.

[abhishek-nexthop]

Description of PR

Introduce complete QoS remapping test framework for SONiC that validates DSCP-to-TC mapping, TC-to-Queue mapping, and TC-to-DSCP mapping functionality with packet capture verification.

• Phase 1: Queue counter validation
• Phase 2: DSCP remapping verification via packet capture

Key Components:

• qos_remap_config.json with REMAP_TEST profile for all three QoS mappings
• Helper functions for queue counters, DSCP lookup, and packet capture
• Automatic cleanup fixture ensuring clean test state

Summary:
Complete QoS test infrastructure with packet-level DSCP verification
Fixes # (issue)

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• New Test case
  • Skipped for non-supported platforms
• Test case improvement

Back port request

• 202205
• 202305
• 202311
• 202405
• 202411
• 202505

Approach

What is the motivation for this PR?

Add a test to make sure custom QoS mappings work properly.

How did you do it?

• Changed QoS mappings for testing
• Sent test traffic through the system
• Checked if traffic goes to the right places based on the new settings

How did you verify/test it?

• Queue check: Looked at queue counters to make sure traffic goes to the correct queue
• DSCP check: Checked outgoing packets have the right DSCP values
• Full test: Made sure traffic flows correctly with custom settings

Any platform specific information?

Works on Broadcom platform

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

Any

[mssonicbld]

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[mssonicbld]

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