Feat(eos_designs): Add support for mlag_peer_ipv6_pool

[Xatrekak]

Change Summary

This PR adds support for configuring the L2 MLAG peer via IPv6. This is accomplished by adding new input-variables and the supporting infrastructure:

• mlag_peer_address_family
• mlag_peer_ipv6_pool
• ipv6_prefix_length

Related Issue(s)

#3715

Component(s) name

arista.avd.eos_designs
arista.avd.eos_cli_config_gen (Documentation only. No logical changes to component.)

Proposed changes

This changes adds the capability to configure the MLAG peer using IPv6. To accomplish this a new input variable has been created that allows the selection of an address family via mlag_peer_address_family.
In addition to this mlag_peer_ipv6_pool has been added to specify the IPv6 pool to use.

l3leaf:
  defaults:
    mlag_peer_address_family: ipv6
    mlag_peer_ipv6_pool: 2001:DB8::/56

The default subnet when creating peers has been set to /64 following the current IPv6 best practices, however this is configurable via ipv6_prefix_length e.g:

fabric_ip_addressing:
  mlag:
    ipv6_prefix_length: 127

How to test

molecules have been created and ran:
molecule converge -s eos_designs_unit_tests -- --limit MLAG_IPV6

This has also been ran in a lab environment running vEOS and CVP. This feature has been built and successful tested against a local AVD enviroment setup in this lab.

leaf2#show mlag
MLAG Configuration:              
domain-id                          :        DC1_L3_LEAF1
local-interface                    :            Vlan4094
peer-address                       :         2001:db8::1
! Output omitted
MLAG Status:                     
state                              :              Active
negotiation status                 :           Connected

Limitations

This has not been tested in the scenario where both the normal MLAG peer and the L3 MLAG peer both use the same SVI and is likely unsupported currently.
This scenario will be tested and resolved in a future PR that adds support for configuring the L3 MLAG peer with IPv6.

Checklist

Repository Checklist

• My code has been rebased from devel before I start
• I have read the CONTRIBUTING document.
• My change requires a change to the documentation and documentation have been updated accordingly.
• I have updated molecule CI testing accordingly. (check the box if not applicable)

[ClausHolbechArista]

LGTM. Thanks! Please make sure someone tests this including on EOS so we know the generated config is valid.

[ClausHolbechArista]

Since you are changing the order of structured config, you also get the "joy" of having to rerun all our molecule tests locally.

cd ansible_collections/arista/avd/molecule
make refresh-facts

[jerryatarista]

LGTM