Re-instate "cfe_platform_cfg.h" and "cfe_mission_cfg.h" samples

[jphickey]

Is your feature request related to a problem? Please describe.
These files are no longer necessary, but are still supported/usable for compatibility with existing configurations. Some long-time users expressed concern about their disappearance from the source tree.

Describe the solution you'd like
As a transitional measure, keep a copy of these files in the sample_defs directory, which shows that they are still usable.

Describe alternatives you've considered
N/A

Requester Info
Joseph Hickey, Vantage Systems, Inc.

[jphickey]

Unfortunately this creates some complexity with workflows - they will end up using the version in sample_defs instead of the default. Workflows should use the default copy.