add more granularity to reissue-certificates action

[Garrett Neugent]

Currently, the reissue-certificates action defaults to reissuing certs for all applications that are related to vault. Instead, it would be great if the operator could to pass a list for specifying which applications, so there is more control, e.g:

juju run-action vault/leader reissue-certificates apps=aodh,openstack-dashboard,nagios

If this is adopted, it would be great to also have an `--all` flag, to handle the intended cases where all applications need a new certificate.

Thanks for your time!

[Billy Olsen (billy-olsen)]

This will be a bit tricky to implement, especially for any models which are in a cross-model relation as the remote application name is not necessarily known to Vault, so the user experience will be confusing.

I agree that this would be a good feature to implement, but will need to review possible options of what might work here.