:sparkles: Add asset Generator.

[jortel]

Add a asset generator model, REST resource and API endpoint:

• /asset/generators
  • filter: name, kind

AssetGenerator (model):

• name
• kind
• repository Repository
• variables any
• parameters any
• identityID uint
• identity ->Identity
• assetGeneratorID uint
• assetGenerator ->AssetGenerator

AssetGenerator (resource):

• name
• kind
• repository Repository
• variables Map
• parameters Map
• identity Ref

The kind will be mapped to an addon using a selector.

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