As this plug is called on every request, this should reduce load on the
database by not requiring to select on the users table every single
time, and to instead use the by-ID user cache whenever possible.
This fixes a race condition bug where keys could be regenerated
post-federation, causing activities and HTTP signatures from an user to
be dropped due to key differences.
User keys are now generated on user creation instead of "when needed",
to prevent race conditions in federation and a few other issues. This
migration will generate keys missing for local users.
Non-Create/Listen activities had their associated object field
normalized and fetched, but only to use their `id` field, which is both
slow and redundant. This also failed on Undo activities, which delete
the associated object/activity in database.
Undo activities will now render properly and database loads should
improve ever so slightly.
