Add independent_entries capability

[damooo]

Independent entries imply, one can create/delete an entry/object without checking for existence of any other entry, and with out create/delete -ing any other entry.

Few backends doesn't support independent entries.

For example in fs backend:

• One cannot create an object, with out creating it's parent dir object.
• One cannot delete a dir object, without deleting all of it's descendents.

Knowing this information is crucial to properly managing logic and locking at application layer.

[Xuanwo]

The capabilities must be mutually orthogonal to each other. Therefore, we cannot add independent_entries directly. Perhaps we should consider splitting them into other capabilities or approaching the problem from a different angle.