develop: Add field to RobotState to track command completion

[chianfern]

New feature implementation

Implemented feature

Added command_completed, a boolean that indicates the completion of the current command.

Implementation description

Previously, if a command was completed, the RobotState's command_id should be a nullopt. This led to the issue where if a new command is issued and instantly completed, the following RobotState would have a null command_id and users of the free_fleet Manager would be unable to determine if the command was successful or was not received.

With the new command_completed field, the completion status is explicit and command_id always has the id of the latest command.

[aaronchongth]

Closing with #145