Data, validation, and API documentation overhaul tracker

[danswick]

This ticket is to track all requests and known issues related to data and API docs, to be picked up as something like an Epic when the team has capacity. When new requests or issues come in, let's track them here so we can plan a larger scope of work later.

List of rollup tickets:

• Update headers in data dictionary to match up w terms used in SF-SAC #3895
• Improve FAC Data Dictionary #4352
• Create data field mapping page #3789
• Document known data issues #3788 (keeping this one open while @gsa-suk uses it to track data issues)
• Create submission field validation documentation resource page #3787
• Data reliability documentation #3871