Add providers level to skills

[louistiti]

To make sure we don't overuse intents, we should add a provider level to skills. This will improve the NLP model accuracy.
In this way, a "Music" skill can be created with nearly the same intents but for different providers such as Spotify, Pandora, Deezer, etc.

• The provider can be defined on the fly using slot filling/entity annotation on the utterance sample.
• A provider is set by default in the config of the skill.
• Build facade system for SDKs so it becomes a common practice when developing skills with providers?
• Make use of enum entities to define a provider?

[louistiti]

✨ [1.0.0-beta.10] Add providers level to skills