[FEAT] store.pushOperations for `remove` operations

[runspired]

json-api is introducing operations. The ember-data team would like to introduce a new async API (store.pushOperations) for handling a subset of these operations. For the time, this subset would be remove operations; however, operations on relationship membership changes should also be considered.

Operations for creating and editing records would not be allowed, as push and pushOperations are APIs for updating the state with "known good" state, so contextually, performing "local state" operations via this API would not make semantic sense.

This API would return a promise that resolves upon completion of the operations or rejects with any failures. As per json-api spec proposal, all operations must succeed, or they all fail.