Add l10n workflow to build translated docs

[rffontenelle]

The idea is to generate translated documentation and to check translation links whenever translation files is changed. This is in a draft state, and is set to build every language, which is not ideal.

Need to figure out: how to check changed files in the commit (on both push and pull_request events) so that I can filter the language codes that should trigger build.

See this example of workflow run.

This is particularly useful for pull request to pop up errors for the translator.