Add RS384 support for OIDC flow

We have a client that wants to use Quay with an OIDC provider that uses RS384 encoding for their JWT tokens. Currently, Quay only supports hs256 and rs256 encoding methods.  These methods are defined here:

https://github.com/quay/quay/blob/f774e4c6b6c674c822057a1d3dd49a3d5c36e6ca/util/security/jwtutil.py#L29

https://github.com/quay/quay/blob/f774e4c6b6c674c822057a1d3dd49a3d5c36e6ca/oauth/oidc.py#L27

Client already changed these values manually and OIDC appears to be functioning properly.