Further break down message module to facilitate customization

[skliper]

Is your feature request related to a problem? Please describe.
Currently customization of the monolithic message module can either be done by "cherry-picking" code from the core and customizing/adding/replacing whatever needs to be customized or "clone-and-own" the entire module. "Cherry-pick" is fragile since it depends on the internal file layout and structure of the message module (implementation), "clone-and-own" is a lot of duplicated code and the possibility of divergence from core development.

It's a similar concept as for a custom OSAL depending on shared or portable elements in the repo, in that cherry-picking is dependent on implementation, not just APIs and the alternative is clone-and-own.

Describe the solution you'd like
Break the message module down into the different parts of the header - CCSDS Primary, CCSDS Extended, CFS Secondary such that they can be included by projects as building blocks, and the "cherry-pick" vs "clone-and-own" is then in the context of smaller modules. Basically if a project wants to customize just the time format, they could either clone-and-own the CFS Secondary implementation or cherry pick. The primary and extended headers could be used as is.

Describe alternatives you've considered
Approach is a project trade, this change makes that decision a smaller impact (less code either way). The code was separated parts of the header by file already as part of #726 to make cherry-picking easier (and secondary is separated by field in the header), but also makes breaking into separate modules easier.

Additional context
#726, #801
#726 (comment)

Requester Info
Jacob Hageman - NASA/GSFC