It's been a sufficient amount of time since support for these variables
has been removed; users should no longer require an explicit error to
remind them to use `--user` from now on.
Fixes#115.
The recyclarr docker image no longer requires root.
- `PUID` and `PGID` environment variables are no longer used.
- `recyclarr.yml` is no longer created if it is missing.
Fixes#102
The non-root user and group were still being created in the Dockerfile,
which means that if the PUID or PGID were modified, those changes would
not be processed.
This change completely removes the `adduser` / `addgroup` commands and
instead the user spec is passed directly to `su-exec`.