Add CC licenses text label to plugin settings

[frankstrater]

Although the plugin uses this default new list for the textual representation of the licenses, we could register them as plugin setting, so admin users can change it through the plugin settings interface.

https://docs.joinpeertube.org/contribute-plugins?id=settings

CC BY 4.0
CC BY-SA 4.0
CC BY-ND 4.0
CC BY-NC 4.0
CC BY-NC-SA 4.0
CC BY-NC-ND 4.0
CC0 1.0
Public Domain Mark 1.0