LG-11006: "User registration complete" event not logged for direct sign-up

[jc-gsa]

🎫 Ticket

LG-11006

🛠 Summary of changes

Adds the event "User registration: complete" to user registration flows where previously missing.

[aduth]

I think this direction makes sense as far as treating the MFA selections setup as funneling toward the completions screen, which is how we're using it today.

In the future we might want to be able to support sending people to the MFA selection setup outside these flows (I recall this coming up in the designs around #8965 and why we couldn't link "choose another authentication method" in the error alert). Maybe we'd want to use the newly-introduced user_session[:in_account_creation_flow] in the logic to support that.

This also has me realizing that our idea of "setup completion" is rather inconsistent, since it's less to do with account setup, and more to do with whether someone needs to see a consent screen, which can happen outside initial account setup. That caught me off guard here since I worried about sending people to the "setup completion" in a flow like the AAL2 strict upgrade, but I think this is consistent with how we're currently treating "completions".

Those are things we can follow-up with separately and wouldn't block this, but I think this work helps highlight a lot of existing inconsistency.

[aduth]

Can we add some regression test coverage for the event being logged for sign-in?

Edit: Also, would help for review to complete the PR template details.

[aduth]

LGTM 👍