Clearing consent

[Cantor, Scott]

Pertains to IDP-748, you'll see a lot of discussion and a number of semi-non-useful commits from me, but TL;DR I think we need to work on a subflow to clear consent state rather than rely solely (or maybe even at all) on a query parameter to do it.

Longer term I know we need to get a management UI together for all this anyway, but in the meantime I'm just thinking a flow we can run to clear it, and then do a relative-path redirect back into where we started.

We could do a subflow, but I think orchestrating that in the middle of the login process would be ugly and pretty invasive, much like all my attempts at making the current query parameter work.

I'm thinking of just starting a flow that would eventually become the user UI and just implementing this one simple operation for now.

-- Scott