[Feature Request] Support for URL-Base for use in reverse proxy configs

### Description

Add support for reverse-proxy, by providing a configurable URL-Base

### Desired Behavior

Make the URL-base configurable so that Agregarr can be accessed from http://agregarr.url:7171/URL-base instead of http://agregarr.url:7171/

### Additional Context

I like to have all my dashboards behind a reverse proxy, this enables me to expose all running services from one url and port. for example in my setup sonarr is accessible from https:///sonarr, radarr is accessable from https:///radarr, and i would like to have Agregarr available from https:///agregarr. Using this method requires some support at the side of the webap/service (in this case Agregarr) to support a custom URL-Base.