Allows clients to observe the status of their submissions. Commands may be submitted via the Command Submission Service. The on-ledger effects of their submissions are disclosed by the Update Service. Commands may fail in 2 distinct manners: 1. Failure communicated synchronously in the gRPC error of the submission. 2. Failure communicated asynchronously in a Completion, see completion.proto. Note that not only successfully submitted commands MAY produce a completion event. For example, the participant MAY choose to produce a completion event for a rejection of a duplicate command. Clients that do not receive a successful completion about their submission MUST NOT assume that it was successful. Clients SHOULD subscribe to the CompletionStream before starting to submit commands to prevent race conditions.
