When using PATs if the user that the PAT is for has been removed, we
currently log the missing user at ERROR level. Since this is not
something our SREs can fix, this PR downgrades the NotFoundError to
WARN, instead of ERROR.
* Middleware first version
* Middleware tests
* Add tests
* Finish middleware tests
* Add type for request
* Add flagresolver
* Fix snapshot
* Update flags and tests
* Put it back as default
* Update snapshot