Failing tests should direct contributors how to fix them

[james-garner-canonical]

Description

• In particular, I'm thinking the CLA check could link to the page where you can sign the agreement
  • https://ubuntu.com/legal/contributors/agreement
• The conventional commits test should link to the Juju project's specification for conventional commit types
  • https://github.com/juju/juju/blob/main/doc/conventional-commits.md
• The unsigned commits check could link to somewhere like
  • https://docs.github.com/en/authentication/managing-commit-signature-verification/signing-commits

We could also put some information about this and about whether to expect integration tests to pass in the PR template since user's will see that information when they make a PR

• https://github.com/juju/python-libjuju/blob/main/.github/pull_request_template.md