Fix #1708, Align padding explicitly in cfe_tbl_msg.h

[thnkslprpt]

Checklist

• I reviewed the Contributing Guide.
• 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

• Fixes Implicit padding in CFE_TBL_HousekeepingTlm_Payload_t #1708
  • The 2-byte implicit padding in CFE_TBL_HousekeepingTlm_Payload_t as noted in the issue has been made explicit, and my testing showed 2-byte implicit padding on the end of CFE_TBL_TblRegPacket_Payload_t as well, which has also been rectified and made explicit.

Note: If this is merged, it will require updates to cfe-tbl-hk-tlm.txt in the Ground System tool to ensure clean and correct interpretation of the data members.

Testing performed
GitHub CI actions all passing successfully.
Local testing confirms all cFS bundle tests passing and coverage unaffected.

Expected behavior changes
Compilers trying to align to 32-bits will not longer add implicit padding in these 2 locations.

System(s) tested on
Debian GNU/Linux 11 (bullseye)
Current main branch of cFS bundle.

Contributor Info
Avi Weiss @thnkslprpt

[thnkslprpt]

There are a few other cases of implicit padding in the msg structs in the other cFE modules.

See quick-fixes here which make all compiler-added padding explicit in the msg files: main...thnkslprpt:cFE:fix-padding-issue-in-msgstruct-files
(There was also CFE_SB_RouteCmd_Payload_t which seems to have an unnecessary spare byte there...)

Should I add those on to this PR or just open a new issue?