Use case:
User with `create_doc` index privilege will be allowed to only index new documents
either via Index API or Bulk API.

There are two cases that we need to think:
- **User indexing a new document without specifying an Id.**
   For this ES auto generates an Id and now ES version 7.5.0 onwards defaults to `op_type` `create` we just need to authorize on the `op_type`.
- **User indexing a new document with an Id.**
   This is problematic as we do not know whether a document with Id exists or not.
   If the `op_type` is `create` then we can assume the user is trying to add a document, if it exists it is going to throw an error from the index engine.

Given these both cases, we can safely authorize based on the `op_type` value. If the value is `create` then the user with `create_doc` privilege is authorized to index new documents.

In the `AuthorizationService` when authorizing a bulk request, we check the implied action.
This code changes that to append the `:op_type/index` or `:op_type/create`
to indicate the implied index action.