Add script to set appropriate permissions on /dev/dri/* devices

[kabadisha]

I have been investigating how to enable hardware acceleration and found that it requires the www-data user to have permission on /dev/dri/* devices. A lot of people seem to be happy to just set the permissions to 666 on /dev/dri*, however that doesn't seem like a great solution.

In the end, I found a really elegant solution to the permissions issue that the guys over at linuxserver used for their Plex image.

The script is a direct clone of their version, I have just added some echos to show what is going on and changed the user to the www-data one we use for ZoneMinder.

It adds the www-data user to the appropriate group(s) if they already exist or creates new groups as required.
This has the benefit of meaning that you don't have to mess with the permissions of the /dev/dri/* devices on the host.

Hope this makes sense.

FYI, this is my first PR to an open source project, so apologies if I missed any steps or etiquette.

[dlandon]

I'll take a look at this.