[fix] Perforce auth provider panics when only IP is provided

[pjlast]

When only an IP address and port (like 127.0.0.1:3080 is provided as p4.port, the auth provider will panic since the value can't be parsed as a URL correctly. This is common to do when talking to Perforce, because the p4 CLI automatically prefixes tcp: if this is the case.

However, we can't quite do this because the auth provider URL and the code host URL need to match, so if we auto-adjust the auth provider URL they will no longer match.

This PR adds error handling on the auth provider, and will display a more helpful error message instead of panicking.

Test plan

Unit test added

Changelog

[Rhia2]

This LGTM. Thank you

[mmanela]

Should we clarify this in our docs too?