Refactor and simplify Microsoft.Identity.Test.LabInfrastructure

[Avery-Dunn]

Continues the lab migration work begun in #5558 and other PRs based on discussions and similar refactoring done in AzureAD/microsoft-authentication-library-for-java#1002

In short, these changes remove the last pieces of the old API-based system of retrieving test config in favor of the new key vault-based approach, and should make the Microsoft.Identity.Test.LabInfrastructure package easier to maintain going forward by simplifying the various helper classes/methods

Although a lot of files were changed, the majority of them don't need a deep review: they are test classes that were only changed to use the new helper class/method names and behavior, each file received the same sort of adjustment, and no test behavior was actually changed.

The only files that need a real review are in the Microsoft.Identity.Test.LabInfrastructure namespace, and here is a brief summary of the changes:

• Simplify the helper classes/methods and clarify what they are doing, and allow integration tests to retrieve only the configuration they need
  • LabResponse: Previously just a container for user/app/lab config JSON classes, deleted in favor of separate XYZConfig classes
  • AppConfig and UserConfig: Represents the JSON-based configurations stored in the key vault
  • KeyVaultSecrets: Added to store the names of secrets in our key vaults, rather than hardcoding them in helper methods
  • KeyVaultSecretsProvider: Minor changes to comments to clarify what the key vaults are used for
  • LabResponseHelper: The main helper for retrieving configuration from the key vault, and the class that received the most meaningful changes
    • Renamed from LabUserHelper, as it does more than user config
    • Removed numerous GetXYZUserAsync methods which had hardcoded secret names and, despite the name, returned a merged response containing user, app, and lab configuration
    • Added GetUserConfigAsync and GetAppConfigAsync methods to return separate XYZConfig instances based on key vault secret names
    • Added three ConcurrentDictionary fields to cache deserialized JSON config responses from the key vault
• Remove the last references to the Lab API
  • LabApiConstants: Previously stored query parameters and other constants for API calls, deleted because those calls are no longer made
  • LabServiceParameters: Previously stored numerous enums that were compared to results in API calls, deleted in favor of a simpler LabConstants file as the vast majority weren't actually used
  • LabConstants: Remnants of the enums that were in LabServiceParameters, left here to avoid changing tests and making this PR even larger
  • LabServiceApi: Previously was the main API helper class, deleted because those calls are no longer made
  • UserQueryParameters and LabUserNotFoundException: Previously used only to help format a strings in a few debug logs, deleted in favor of simpler error message behavior

[bgavrilMS]

@MZOLN @gladjohn @cpp11nullptr - can you please review this as this introduces breaking changes to the lab API

[RyAuld]

Reviewed changes with Bogdan during labsync.