feat: Improve Initialization process

[ahmednfwela]

Description

currently the initialization process does the following:

1. make sure the discovery document is fetched (and cached).
2. Load any previously stored id/access tokens, AND make sure they are still valid.
3. Handle any pending logout requests that are received via the front channel logout spec.
4. finalize pending login attempts by loading states (specifically when using same-tab login flows)

New Requirements

• Additional customization
  • The package should give control in decision making to the developers, some examples are:
    • Whether the loaded tokens are valid or not.
    • Whether the invalid tokens should be removed or not.
  • Allow the existence of multiple user managers, where each can manage multiple access tokens feat: OIDC conformance tests #232 docs!: Document multi-manager support #234
  • Introduce hooks to give control to the developer for different parts of the auth flow (feat!: support hooks #228)
• Refactors
  • Remove dependency on flutter_appauth for android and ios/macos

Additional Context

Add any other context or screenshots about the feature request go here.

[dupuisdavid]

Thank you for your feedback @ahmednfwela.
I'm staying tuned.