peertube role API refactor

While exploring peertube role (#1 (closed)), it works quite well, but lacks of full customization. Particularly production.yaml configuration file is only partially templated, ano there are some weird structures, such as a list of peertube_domains, where only the first is useful.

Therefore, full customization would require a refactor more than just an extension of the API.

As its extension states, production.yaml is the definition of a yaml structure. Role variables would worthily reproduce the same yaml structure, instead of splitting parameters into separate variables.

Instead of a templating production.yaml, we could worthily dump it from role's similar variables, with a to_nice_yaml filter.