Feat(eos_designs): add option uplink_mtu under the node config

[kmueller68]

Enhancement summary

It is currently not possible to set the uplink mtu to dedicated leaf node or node group.

Add uplink_mtufor node_group and node settings.

Which component of AVD is impacted

eos_designs

Use case example

    - group: DISTRI_12
      bgp_as: 65412
      uplink_mtu: 9000
      filter:
        tenants: [all]
      nodes:
        - name: distri-12-01
          id: 11
          mgmt_ip: x.x.x.x
          uplink_switch_interfaces: ['Ethernet9', 'Ethernet9']
        - name: distri-12-02.LAN.MU
          id: 12
          mgmt_ip: x.x.x.x
          uplink_switch_interfaces: ['Ethernet10', 'Ethernet10']

Describe the solution you would like

 # Define variables related to all nodes part of this group.
 node_groups:
     # Override the default `uplink_mtu` set at the `node_type_key` level.
     uplink_mtu: <str>

     # Define variables per node.
     nodes:
         # The Node Name is used as "hostname".
       - name: <str; required; unique>

         # Override the default `uplink_mtu` set at the `node_type_key` level.
         uplink_mtu: <str>

Describe alternatives you have considered

No response

Additional context

No response

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