Rename cf_cmd.c file to cf_cmds.c

[thnkslprpt]

Checklist

• I reviewed the Contributing Guide.
• I performed a cursory search to see if the bug report is relevant, not redundant, nor in conflict with other tickets.

Describe the bug
cmd.c file should be renamed to cf_cmds.c to be consistent with the rest of the mainline cFS apps

Code snips

Expected behavior
The inconsistency can make debugging/maintenance harder when using multiple apps

Reporter Info
Avi Weiss   @thnkslprpt