chore: use charmcraft 3

[wallyworld]

We can only currently build for one base, but we can remote build on launchpad and thus get builds for all supported arches.

To publish the charm, we need to manually update the manifest to add support for 20.04 and 22.04, until a decision is made about supporting multiple bases. Or we may need to manage separate charmcraft.yaml files.

The manual steps to do this were as follows:

charmcraft remote-build --launchpad-accept-public-upload

This will run builds on lp for the 4 supported arches and the end result is 4 charm files downloaded locally.
Unzip these charm files and edit the manifest.yaml to add support for both 22.04 and 20.04. Rezip the charm files.
Then the charms can be uploaded to charmhub:

charmcraft upload --name juju-controller --release 3.6/stable <charmfilename>

TODO - need to replace the Build Charms code with charmcraft remote-build

[manadart]

Can you change this to a draft while it's in a fluid state?