properly validate git repository URLs everywhere

[Panaetius]

There is a discrepancy in endpoints dealing with repository URLs.

E.g. PATCH on api/data/projects/<project id> allows setting a repository like [email protected]:SwissDataScienceCenter/renku-data-services.git

But then querying api/data/repositories/git%40github.com%3ASwissDataScienceCenter%2Frenku-data-services.git gives a 422 error Sentry issue: RENKU-DATA-SERVICES-1A

We should go over all the places where we use git repository URLs and make sure validation rules are aligned.