Changes the discharge endpoint

[alesstimec]

Description

The discharge endpoint will now accept only is-consumer <user tag> <offer uuid> format of the caveat.
If user has consumer relation to the application offer, the discharge macaroon will contain a delared caveat offer-uuid <offer uuid> to maintain compatibility with juju controllers.

Engineering checklist

Check only items that apply

• Documentation updated
• Covered by unit tests
• Covered by integration tests

Test instructions

Notes for code reviewers

[github-actions]

⚠️ This PR contains unsigned commits. To get your PR merged, please sign those commits (git commit -S --amend --no-edit) and force push them to this branch (git push --force-with-lease).

If you're new to commit signing, there are different ways to set it up:

Sign commits with gpg

Follow the steps below to set up commit signing with gpg:

1. Generate a GPG key
2. Add the GPG key to your GitHub account
3. Configure git to use your GPG key for commit signing

Sign commits with ssh-agent

Follow the steps below to set up commit signing with ssh-agent:

1. Generate an SSH key and add it to ssh-agent
2. Add the SSH key to your GitHub account
3. Configure git to use your SSH key for commit signing

Sign commits with 1Password

You can also sign commits using 1Password, which lets you sign commits with biometrics without the signing key leaving the local 1Password process.

Learn how to use 1Password to sign your commits.