staticd: support graceful restart in zebra

[jyuan-panw]

Register graceful restart capability with zebra to avoid static routes being deleted immediately in zebra upon staticd restart

[donaldsharp]

Graceful restart is not typically enabled by default. Why do we not have a cli for this behaviorial change?

[jyuan-panw]

Hi Donald, thanks for your review. Could you also suggest the cli syntax for enabling staticd graceful restart? thanks!

[jyuan-panw]

@donaldsharp , how about using this: "static-routing graceful restart"?

[donaldsharp]

Consensus during the tech meeting is to default with this feature on but a way must be provided to the end operator to turn off the graceful restart if it is not wanted. Additionally this change in behavior needs to be documented in the staticd daemon

[enkechen-panw]

Currently there is only one config for staticd, and it is in YANG.

For simplicity, would it ok to let zebra handle the feature directly, that is, make it a zebra-command?

[github-actions[bot]]

This pull request has conflicts, please resolve those before we can evaluate the pull request.