Is your feature request related to a problem? Please describe.
If you use a reverse proxy in front of the FreshRSS "edge" Docker image with OpenID Connect (OIDC) enabled through Docker environment variables, you will repeatedly get these console messages upon site access:

freshrss  | [Mon Jul 10 00:24:19.605840 2023] [auth_openidc:warn] [pid NNN] [client 172.NNN.NNN.NNN:59072] oidc_check_x_forwarded_hdr: header X-Forwarded-Host received but OIDCXForwardedHeaders not configured for it
freshrss  | [Mon Jul 10 00:24:19.605842 2023] [auth_openidc:warn] [pid NNN] [client 172.NNN.NNN.NNN:59072] oidc_check_x_forwarded_hdr: header X-Forwarded-Proto received but OIDCXForwardedHeaders not configured for it

Describe the solution you’d like

The FreshRSS Docker image should have a "REV_PROXY" variable that, when set to "true", adds "OIDCXForwardedHeaders" and any other requisite configuration to the Apache configuration file.

Describe alternatives you’ve considered

The alternative is to write a custom Apache configuration file with the reverse proxy changes and bind mount that custom file into the image at "/etc/apache2/sites-available/FreshRSS.Apache.conf".

Additional context
We're using Caddy as the reverse proxy and Keycloak as the OpenID server.