Add UserConfirmed workflow event for user email confirmation

[davidpuplava]

Context

SaaS and newsletter websites send user registration emails to the registered email address to confirm user ownership of the entered email address. OrchardCore does this out of the box.

After a user confirms ownership of an email address, it is common to send a "Welcome to the site!" email welcoming the new user.

Rationale

While it may be possible to construct a timer workflow to determine when a user has confirmed their email address, a more straightforward approach is to trigger an event when a user confirms their email, which can then be used to send the email.

This PR intends to implement that.

Here is a GIF demonstrating that experience, and showing the new User Confirmed workflow event:

[MikeAlhayek]

Please also add this new change to the 2.0.0.md release notes.

Lastly, instead of using UserContext I would suggest using a new ConfirmedUserContext class that would inherit from UserContext with one more property "ConfirmationType" This conformation type would have Email or Phone this way we can utilize this event to also confirm phone in the future. I would not add "Phone" in this PR, but I would add the type of the confirmation.

[github-actions]

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