Utility endpoint to submit a batch of sequenced, dependent requests.

The requests are guaranteed to be performed sequentially in the order given in the request and will abort if any request does not return a status-2xx response. For example, this can be used to ban and delete all of a user's messages by sequencing the ban followed by the delete_all: if the ban fails (e.g. because permission is denied) then the delete_all will not occur. The batch body and response are identical to the /batch endpoint; requests that are not carried out because of an earlier failure will have a response code of 412 (Precondition Failed)."