Introduce a config option to set the script path

[leahoswald]

I'm currently running my radicale on a subfolder at a hoster (uberspace) where I can't modify the proxy headers with X-Script-Name. This breaks the web interface and most likely everything else because of wrong paths or redirects, because radical is always assuming to run at the root without this header. I modified this line in my copy of radicale to base_prefix = "/radicale" and this works (assuming radical is running at example.com/radicale/).

Modifying the source locally isn't that great and I would like to propose a new config option in the server block named script_name_path. This way I could set the value via config file instead of the header by a variable with a similar naming.
I would change the code in a way to chose the config option or its default value if no header is present, preserving the current way the things work.

I would also write a PR if there is any chance that this proposal will be accepted.

[pbiering]

I would assume, an additional option while keeping default if not enabled is not a problem. PR for source and documentation (md) would be welcome.

Currently I see more a problem merging the PRs into main respository, as the Kozea team is quiet since some time and other PRs are already open since weeks/months.

[pbiering]

Please create PR