Integrate capabilities into OPA ecosystem

[srenatus]

With #78, we've got a caps file for swift-opa. It would be nice to integrate that somehow into the OPA ecosystem.

• opa build (or Regal?) could come pre-seeded with swift-opa caps,
• We could render tags on the builtins docs (docs: report builtin availability in other interpreters opa#8228)
• ...or link/publish them through the OPA website.

[anderseknert]

Yes, definitely want this in Regal. Should be fairly straightforward following the pattern we used for EOPA. We have tags / releases here now?

[srenatus]

Soon, #83!

[philipaconrad]

One thing we may want to resolve before publishing capabilities everywhere-- the JSON capabilities dump from swift-opa puts the keys in different order to how OPA does it. From what I can tell, Go/OPA goes in struct field order, and Swift seems to be dumping fields in sorted order. Not sure if that'll be an issue downstream, but it surprised me when I was looking at a capabilities diff between Swift OPA and OPA today.

EDIT: This thing I thought was an issue turned out to be a nothingburger, and was resolved by the end of #86. We do emit JSON fields in a different order (all keys sorted), but it's fine. As long as folks are doing a JSON diff, and not a raw text diff, they should be fine.

[philipaconrad]

As of 0.0.2, we do have tags and releases now, although capabilities files are not provided as a release artifact just yet.