feat: Add terraform-deploy reusable workflow

[orfeas-k]

Add terraform-deploy.yaml reusable workflow that deploys the charm using
the terraform module and waits for environment steady state. This essentially
transforms https://github.com/canonical/sunbeam-terraform/blob/main/.github/workflows/deploy.yml
into a reusable workflow. As per juju-wait help command, the environment is
considered in a steady state once all hooks have completed running and there
are no hooks queued to run, on all units. This means that the check will succeed
if the charm units go to idle.

Add terraform-apply.yaml reusable workflow that applys the TF module and
using juju wait-for, waits for the application to go in active or `blocked.

[mvlassis]

@orfeas-k It seems you are using the juju-wait executable to wait until the desired state has been achieved. On the plugin's main page it is stated as outdated, and instead it is suggested that we move to the juju wait-for subcommand. Perhaps that is something you can look into?

This way we can avoid having to install an additional snap package.

[DnPlas]

Thanks @orfeas-k , looking good already, just a comment on making sure this works in multi charm repos.