AddSubCmd adds a sub-command closure to the workload cli.

CmdHelper handles common workload command logic, such as error handling and ensuring the database name in the connection string (if provided) matches the expected one.

HandleErrs wraps a `RunE` cobra function to print an error but not the usage.

ParseOutput reads the output of a workload run and returns the list of valid Ticks it contains.

SetCmdDefaults ensures that the provided Cobra command will properly report an error if the user specifies an invalid subcommand.

WorkloadCmd returns a new command that can serve as the root of the workload command tree.