Add "Payload" sub structure for HK

[Joseph Hickey]

Is your feature request related to a problem? Please describe.
To comply with CFE/CFS typical patterns, the HK TLM structure should put its information in a sub-struct called "Payload" (as opposed to having fields at the top level)

Describe the solution you'd like
Move items into Payload sub-struct

Describe alternatives you've considered
N/A

Additional context
Does not change content - This naming convention / sub-structure is necessary to work with some tools

Requester Info
Joseph Hickey, Vantage Systems, Inc.