Bump the `build-on`/`run-on` base for all Charmed Kubeflow charms

[ca-scribner]

Context

Most (all?) of the Charmed Kubeflow charms use Ubuntu 20.04 for their base image. At some point in future, 20.04 will drop out of support for Juju. As part of Charmed Kubeflow 1.9, we should bump these bases to 24.04

In the past we've discussed this and hit some issues:

• Here is a discussion we had in the past
• And here is a relevant issue

What needs to get done

1. Do a POC, bumping a charm to ensure we can do this successfully and that the upgrade path for the charm works
2. Bump all Charmed Kubeflow 1.9 charms to 24.04
3. Write an upgrade guide

Definition of Done

1. all charms in Charmed Kubeflow 1.9 use 24.04, or have an open issue for any that cannot be bumped
2. documentation exists to migrate a charm from the current base to 24.04

[syncronize-issues-to-jira[bot]]

Thank you for reporting us your feedback!

The internal ticket has been created: https://warthogs.atlassian.net/browse/KF-5582.

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