Generify VS Code extension APIs for better extensibility

Service Catalog Channel API needs to provide a shared value to be used by the editor. This shared value will contain the list of services available in the channel and the channel must be able to updated the existing values when needed (new yaml added, removed...). To achieve that the channel api should have access to the right types in the envelope server in order to notify new value changes. Currently this types are fixed which makes hard to extend.