Implements the Authentication Configuration Checks

[mereghost]

Related Work Package: OP#62100

Implements the OIDC connection tests and some elementary OAuth2 tests.

[NobodysNightmare]

In addition to the 🔴 that I cleverly posted immediately, I added all other traffic light colors to round it off.

In general I like what those validators might look like soonish.

[NobodysNightmare]

🟢 The current implementation of this implies that I can only call register_checks once, never twice.

I think that's enough, but it limits the ways in which I can write my validator a bit. E.g. this layout would not work:

def validate
  register_checks(:common_check)
  if rand < 0.5
    register_checks(*a_checks)
    validate_a
  else
    register_checks(*b_checks)
    validate_b
  end
end

The other issue is that if I for whatever reason don't add any tests, we'd now return nil instead of returning {}. As indicated by the green traffic light, I think both of these problems are absolutely minor, but I wanted to explicitly write them down at least.