Simplify get_tags_from_labels

[Lotram]

A few services were not using the default parameter names for the get_tags_from_labels (pagure and youtrack)

I changed the config param names for those service, while allowing multiple aliases, to ensure backward compatibility.

This allows for a much simpler get_tags_from_labels, only parameters being the labels and the config.
We could even consider moving this function outside the Service class, since it does not depend on the Service subclass (or this could be a ServiceConfig method instead).

[ryneeverett]

• I don't see much point in adding deprecation notices to the documentation. If somebody isn't using the deprecated options then they don't need to know about them. If they are using them then they'll get the exact same information from the log warnings.
• We should add an entry to the api.rst changelog mentioning the addition of render_tags_from_labels. (I'm inclined to think we shouldn't mention deprecated parameters in that changelog. Since deprecations don't necessarily require a version bump, there wouldn't necessarily be any place to log them so we shouldn't set that precedent.)