when authentication fails, check that the username looks like a URL

[diosmosis]

If it does not look like a URL we can report to the user via an error that the username should be a URL to a Matomo instance.

Might reduce some support requests.

[diosmosis]

Looks like we can't even throw an error with a useful error message in this case. Looker Studio will simply swallow the error and say something along the lines of "the connector failed".