[SDK-2399] Add support for Organizations

[frederikprijck]

This PR adds support for Organizations as well as User Invitation (even tho limited because of the nature of how User Invitations works currently and how that makes integrating it in Mobile and Desktop applications troublesome)

• Users can pass organization and invitation parameters to LoginAsync, this will send those parameters to the /authorize endpoint. Note, we have no first-class support
• The org_id claim is validated, only when it was provided to LoginAsync.
• The org_id claim is parsed and made available as part of User.Claims
• Added documentation on how the user can log in to an organization
• Added limited documentation on how the user can accept an invitation, mainly because user invitation is URL based and it's not an easy task to integrate this with WPF, Winforms or UWP and it can also be tricky integrating it with Android or iOS apps.

[frederikprijck]

Added some tests @stevehobbsdev .

[stevehobbsdev]

Thanks @frederikprijck! What about the case for when the requested Org ID doesn't match the one present in the ID token? We cover it in the implementation, just not in the test.

[frederikprijck]

@stevehobbsdev Good call, updated.