Specialize media-type constraints for each FedRAMP resource type

[aj-stein-gsa]

          > Also while working on this last night @david-waltermire, I realized we have a split between NIST and FedRAMP OSCAL values, but the `<base64/>` and `<rlink/>` assemblies do not have a `@ns` to clearly label that split and focus a constraint. It may be necessary to make an upstream issue and possible recommendation here, but I presume we can discuss further as a team at a later date.

I talked to @david-waltermire about this challenge and we are thinking about this constraint the wrong way. We can generally constrain all use of media types different from upstream without @ns, but also wisely limiting to a recommended or allow-list only set of media types only really makes sense specifically for respective attachments (i.e. FedRAMP has a notion of which back/matter-resources or in-line links for policies, user guides, etc., but not which of those have good respective filetypes).

On that note, Dave has asked me to close this PR and not merge, open new issue to track analysis, decision, and a more meaningfully complex set of constraints, not just a general one, for this series of requirements.

Originally posted by @aj-stein-gsa in #644 (comment)

[aj-stein-gsa]

@david-waltermire asked we fast-track this one and move up the backlog to consider.