Add maintainerr.subdomain.conf.sample

[x] I have read the contributing guideline and understand that I have made the correct modifications

Description

Adds support for Maintainerr

All I did was s/foo/bar a few things and remove a few commented lines that said to remove them. I think this should be fine, though!

Benefits of this PR and context

Maintainerr sounds like it could be pretty useful. Since I like to put things like this behind Authentik, and I use SWAG as a reverse proxy for doing so, I wanted to contribute my added proxy conf.

Please note that the only reason I didn't add a subfolder.conf.sample is because I never use subfolders, and so I don't want to add it without testing — I don't see any technical reason why a subfolder conf can't just be added as well, but I'd rather not do it myself.

How Has This Been Tested?

As of writing this, the relevant part of my setup consists of one VM host with a private IP running SWAG as a standalone Docker Compose project, with lines in its docker-compose.yml to add a new bridge network named swag:

#...snip...
services:
  swag:
    networks: ["swag"]
    #...snip...
networks:
  swag:
    name: swag

And then I have in another Compose project:

#...snip...
services:
  maintainerr-service:
    container_name: maintainerr
    networks: ["swag"]
    #...snip...
networks:
  swag:
    external: true

And I also have Authentik running as an external LXC container, which I tested with this setup by uncommenting the relevant lines in the conf.sample file.

linuxserver / reverse-proxy-confs