spar update issuer

[fisx]

https://github.com/zinfra/backend-issues/issues/929

this took about an hour to hack together, and the only thing that's missing is two functions for lookup users on old issuers and for moving them to the new one. and tests. and i did some cleanup on the way. to be specific:

• changed IdP type alias to carry TeamId and [Isuser].
• change db schema to match new type.
• type checker now found some IdPConfig Teamid where the type alias IdP should be used.
• change errors: when trying to update issuer to one that already exists, that's always bad, not only if it's in another team!

now i should probably spend another hour implementing the competing idea of keeping two idps, adding cassandra columns to make the old and the new idp reference each other, and allow for concurrent use of both. right now my gut feeling is that it'll be a lot more work to get right.

UPDATE: I just did them both in one PR, seemed easiest. :)

[fisx]

things to think about more:

• two devices, one using the old login code, one using the new one?
• are login codes cached?
• when do users get logged out and forced to login again?

[fisx]

Any C* experts who would like to comment on e2dddeb? @jschaul?

[fisx]

Any C* experts who would like to comment on e2dddeb? @jschaul?

(I'm happy to give context in a quick phone call tomorrow.)