No ability to pin charm revision

[Nobuto Murata]

https://bugs.launchpad.net/sunbeam-charms/+bug/2066540 is an example.

In an ideal world, we can just follow a channel and it will give us the best experience. In a real world, sometimes we need to specify an exact charm revision.

- if there is a regression, and pin to one older revision until a fix will be released
- creating a staging or UAT environment where the charm revision must be exactly the same as a production environment otherwise no charm upgrade testing can be done
etc.

As of today, Sunbeam doesn't accept a charm revision. e.g.

https://github.com/canonical/snap-openstack/blob/09910fd9f59ea63a1c9bb69c2bba56eb77af2899/sunbeam-python/sunbeam/commands/clusterd.py#L467-L483
(channel and charm config can be specified in manifest.yaml but not revision)

[Hemanth Nakkina (hemanth-n)]

Revision can be set in the manifest for all k8s and machine charms that are driven by terraform-juju-provider. See charms section in [1] on how to set revision.

However as Nobuto pointed out sunbeam-clusterd charm in maas type deployments is driven directly using pylibjuju instead of terraform and the revision is missing.

To summarise, ability to pin charm revision is available for all the charms except sunbeam-clusterd.
This bug is relevant only for sunbeam-clusterd charm.

[1] https://microstack.run/docs/manifest