Bring addon naming in line with Docker mods and themepark docs

[saltydk]

This should change the current output of:

<link rel="stylesheet" type="text/css" href="https://theme-park.dev/css/addons/readarr/readarr-readarr-alt-logo/readarr-readarr-alt-logo.css">

to the correct (when following themepark docs):

<link rel="stylesheet" type="text/css" href="https://theme-park.dev/css/addons/readarr/readarr-alt-logo/readarr-alt-logo.css">

Not super familiar with Traefik plugin development so please do your own test of this.

The PR was made because your own documentation does not line up with the themepark docs: https://docs.theme-park.dev/themes/addons/sonarr/sonarr-4k-logo/#traefik
Which specify it like this:

middlewares:
    sonarr-4k-logo:
        plugin:
            themepark:
                app: sonarr
                theme: base
                addons:
                    - sonarr-4k-logo

This would align both sides with how the Docker mod addons are specified. Feel free to close this if docs get updated instead, have notified the developer.

[packruler]

@saltydk thanks for making this PR!
I added ongoing support for how addons worked prior to this update and added a quick test for the new system.

[packruler]

fixes #15