improve `DiscoveryMethod` classes

[ctrl-f5]

Currently these 3 classes make little sense, the abstract class defines property $wellKnownUri and its getter is calls getWellKnown(), and the subclasses override the property but add a new getter GetWellKnownUri()

Since the 2 implementations have the well-known hardcoded anyway, theres no need for variables. The abstract class can also be made concrete when we allow the $wellKnown to be injected. This way we can use this class directly in our local and test environments by configuring it in the DI container.

[bretterer]

@ctrl-f5 Thank you for the issue report on this. I am going to need to look into this a bit to find why it was created the way it was first. I appreciate your work in your fork on this and in the PR's