Currently, bulk item requests can be any ActionRequest, this commit
restricts bulk item requests to DocumentRequest. This simplifies
handling failures during bulk requests. Additionally, a new enum
is added to DocumentRequest to represent the intended operation
to be performed by a document request. Now, index operation type
also uses the new enum to specify whether the request should
create or index a document.

This commit refactors execution of shard-level
bulk operations to use the same failure handling
for index, delete and update operations.

Currently, update action delegates to index and delete actions
for replication using a dedicated transport action. This change
makes update a replication operation, removing the dedicated
transport action. This simplifies bulk execution and removes
duplicate logic for update retries and translation. This
consolidates the interface for single document write requests.

Now on the primary, the update request is translated to
an index or delete request before execution and the translated
request is sent to copies for replication.

…ification"

This reverts commit 2a651fc.

This reverts commit 42bc2d1.

This reverts commit b5079ce.

This reverts commit eee0d18.