Feat(eos_designs): support for 7300X platform

[markcheverton]

Enhancement summary

Please add Platform 7300X3 to the EOS_Designs - default platform_settings:

We are using these devices as Spines therefore require the management_interface: Management0 defined however don't require MLAG reload timers.

Which component of AVD is impacted

eos_designs

Use case example

Using 7308X3 as Spine in AVD

Describe the solution you would like

platform_settings:
  - platforms: [ '7300X3' ]
    management_interface: Management0

Describe alternatives you have considered

No response

Additional context

No response

Contributing Guide

• I agree to follow this project's Code of Conduct

[tgodaA]

Currently AVD supports custom platform settings. So you can set them in the group vars. Example reference:
https://avd.sh/en/devel/roles/eos_designs/doc/platform-settings.html