net/frr: add graceful-restart to OSPF

[Dennis14e]

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• [x] I have read the contributing guide lines at https://github.com/opnsense/plugins/blob/master/CONTRIBUTING.md
• [x] I have searched the existing issues, open and closed, and I'm convinced that mine is new.
• [x] When the request is meant for an existing plugin, I've added its name to the title.

Is your feature request related to a problem? Please describe. We have a lot of OSPF information in our network with some unstable connections. Graceful restart would help us stabilize the network.

Describe the solution you'd like A checkbox to enable or disable graceful restart and a number input with the grace period (default 120s, 1-1800s).

Describe alternatives you've considered None

Additional context https://docs.frrouting.org/en/latest/ospfd.html#graceful-restart

[AdSchellevis]

https://github.com/opnsense/plugins/pull/4535