Recommend using FcnCode (instead of CommandCode) terminology in the code

[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
Copy of nasa/sample_app#167

Expected behavior
Rename the CommandCode variable in TO_LAB_exec_local_command() to FcnCode to better align with the cFE API.

Code snips

to_lab/fsw/src/to_lab_app.c

Lines 305 to 309 in 9e2ad8c

	void TO_LAB_exec_local_command(CFE_SB_Buffer_t *SBBufPtr)
	{
	CFE_MSG_FcnCode_t CommandCode = 0;
	CFE_MSG_GetFcnCode(&SBBufPtr->Msg, &CommandCode);

Reporter Info
Avi Weiss @thnkslprpt