New CLI command

Subcommands should always be preferred over adding more top-level commands.

Code flow for commands is generally:

CLI (command/) -> API Client (api/) -> HTTP API (command/agent) -> RPC (nomad/)

Code

Consider similar commands in Consul, Vault, and other tools. Is there prior art we should match? Arguments, flags, env vars, etc?
New file in command/ or in an existing file if a subcommand
For nested commands make sure all intermediary subcommands exist (for example, nomad acl, nomad acl policy, and nomad acl policy apply must all be valid commands)
Test new command in command/ package
Implement autocomplete
Implement -json (returns raw API response)
Implement -t (format API response using gotemplate)
Implement -verbose (expands truncated UUIDs, adds other detail)
Update help text
Register new command in command/commands.go
If the command has a status subcommand consider adding a search context in nomad/search_endpoint.go and update command/status.go
Implement and test new HTTP endpoint in command/agent/<command>_endpoint.go
Register new URL paths in command/agent/http.go
Implement and test new RPC endpoint in nomad/<command>_endpoint.go
Implement and test new Client RPC endpoint in client/<command>_endpoint.go (For client endpoints like Filesystem only)
Implement and test new api/ package Request and Response structs
Implement and test new api/ package helper methods
Implement and test new nomad/structs/ package Request and Response structs