Disambiguate command vs message requirements

[skliper]

Is your feature request related to a problem? Please describe.
"Command" terminology has been used for both ground commands (that increment command counters) and inter-app commands (that typically do not increment command counters). So it's unclear in the requirement which sort of use case is intended.

Describe the solution you'd like
"Command" is ground command with additional associated behavior (increments command counters), "Message" is typical sb message that does not increment command counter.

Describe alternatives you've considered
None

Additional context
Discovered during requirements scrub, helps clarify what impacts command counter.

Requester Info
Jacob Hageman - NASA/GSFC