add support for multiple JWT issuers
Our current gitlab instance supports both default JWT tokens and id
tokens. These two types specify issuers gitlab.wikimedia.org
and
https://gitlab.wikimedia.org
respectively.
As we transition from default tokens to id tokens we need to support
both types, but the library we use to validate tokens
(flask_jwt_extended
) does not allow multiple issuers, so we
implement the support directly in reggie at least until the
transition is complete
Bug: T337474