tests: manually test mysql support

Go through all of https://invenio.readthedocs.io/en/master/getting-started/quickstart/index.html with MySQL database (instead of e.g. PostgreSQL).

Afterwards, manually also test :
- account login, signup.
- create a personal access token.
- change password
- change username.

If issues are found, investigate and open an issue and add it to the sprint board.