Add support for JWT based reverse proxy login header

[ruifung]

This enables reverse proxy login via CloudFlare Access.

Or well, in theory, any setup that provides a JWT that is signed by a public key obtainable via a JWKS URL.

Also allows for login header matching against username OR email if desired.

It should be noted that for now, I have not yet gotten around to adding translations for the additional setting items.

[ruifung]

For anyone interested in trying out these changes, I've built and published a docker image with my changes on top of the current Develop branch using the LSIO Dockerfile.

https://github.com/ruifung/calibre-web/pkgs/container/calibre-web