Add Pets management

[djaiss]

This PR will close #626.

Checklist

Before submitting the PR

• Read the CONTRIBUTING document before submitting your PR.
• If the PR is related to an issue or fix one, don't forget to indicate it.
• Make sure that the change you propose is the smallest possible.
• Screenshots are included if the PR changes the UI.

Code-related tasks

• Tests added for this feature/bug.
• Impact on the seeders.
• Impact on the API.

If the code changes the SQL schema

• Impact on account export.
• Impact on importing data with vCard and .csv files.
• Impact on account reset and deletion.

Other tasks

• CHANGELOG entry added, if necessary, under UNRELEASED.
• CONTRIBUTORS entry added, if necessary.
• If it's relevant, add the documentation about your feature in the README file.
• Indicate [wip] in the title of the PR it is is not final yet. Remove [wip] when ready. Otherwise the PR will be considered complete and rejected if it's not working.

[github-actions]

This pull request has been automatically locked since there
has not been any recent activity after it was closed.
Please open a new issue for related bugs.