Enable graceful-restart in OSPF configs via eos_designs

[dgonzalez85]

Enhancement summary

Recently we added support for graceful restart via eos_cli_config_gen:
#4591

When enabling OSPF as the underlay routing protocol in the fabric (underlay_routing_protocol: "ospf"), it would be great that we already set graceful restart by default. This helps with several scenarios, and its set by default when using BGP, so it would align with the same recommendation. It also allows hitless upgrade for Campus scenarios.

References:
https://www.arista.com/en/support/toi/eos-4-15-3f/13744-ospf-nsf
https://www.arista.com/en/support/toi/eos-4-18-0f/13847-ospf-non-stop-forwarding

OSPF and OSPFv3 GR are supported on unplanned software restarts on all platforms.

Which component of AVD is impacted

eos_designs

Use case example

Campus deployments for faster convergece during on unplanned restarts, hitless upgrades, etc.

Describe the solution you would like

Set GR as default for OSPF when setting underlay_routing_protocol: "ospf" in the underlay.

Describe alternatives you have considered

Using this snippet for now:

custom_structured_configuration_router_ospf:
  process_ids:
    - id: 100
      graceful_restart:
        enabled: true

Additional context

No response

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[dgonzalez85]

@pvinci-arista @ksantos01

[pvinci-arista]

This would be a great addition for campus. As this is written, it looks like a breaking change for AVD and would have to wait for 6.0, is that correct? Maybe we can add a key such as underlay_ospf_graceful_restart: false for now and flip the value to true with 6.0?