Redefine Plugin Interface

[JcMinarro]

Plugin interface doesn't apport any value to our SDK, it only asks you to set a name that is not used. On the other hand, the instance of Plugin are used by a code similar to:

val relevantPlugins: List<QueryMembersListener> = plugins.filterIsInstance<QueryMembersListener>()

It is used on that way because "we know" the implementations of Plugin we provide already implement QueryMembersListener interface.

Instead of that, we should include the relevant fun to the Plugin interface and we don't need to filter by checking if implementing a different interface.