FTS - Add the source collection details to the document/hits in search results

In a multi collection index, we need to send the source collection details in to the document matches so that the user can track which collection the document belongs to. This is mandated for the blanket searches on a multi collection index.

The docID query should still work in this case with or without collection scoped searches too.

This could also be configurable -eg: this extra collID decorations needs to be done only if the user has a requirement of blanket searches on the index. If the searches are going to be always collection scoped, then this may turn redundant.