Fix #418, reorganize header files and restructure messages

[jphickey]

Checklist (Please check before submitting)

• [x] I reviewed the Contributing Guide.
• [x] I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution Move the header files to a "config" directory as documented in the CFE guidelines, which allows easier override.

Organize the content to adhere to the patterns.

Specifically - adds a dedicated structure type for each cmd, and also puts the payload into a separate sub-structure.

Command handlers and tests updated accordingly (many of which were simplified).

Fixes #418

Testing performed Build and run all tests Execute local file transfer using 2 instances of CFS + CFDP app

Expected behavior changes Nothing on the external interface changes

System(s) tested on Debian

Additional context First step of making CF adhere to current patterns

Contributor Info - All information REQUIRED for consideration of pull request Joseph Hickey, Vantage Systems, Inc.

[dzbaker]

CCB 30 November 2023: Approved pending rebase.

[jphickey]

@dzbaker -- this is now rebased, should be OK