add "match dscp" support to class map type qos in eos_cli_config_gen

[philippebureau]

Enhancement summary

the current AVD data model does not contain the capability to match class-maps type qos to dscp.

other options like vlan, cos and ip are available

Which component of AVD is impacted

eos_cli_config_gen

Use case example

add dscp to match for class-maps

Describe the solution you would like

proposed data model structure:

class_maps:
  pbr:

      # Class-Map Name.
    - name: <str; required; unique>
      ip:

        # Standard Access-List Name.
        access_group: <str>
  qos:

      # Class-Map Name.
    - name: <str; required; unique>

      # dscp value.
      dscp: <str>

### Describe alternatives you have considered

_No response_

### Additional context

_No response_

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