versioned catalogd https interface RFC

[grokspawn]

We've had some conversations about evolving catalogd's HTTPS service interface in different directions. Such discussions are super-early, but out of them came the observation that status.contentURL could be better suited to support it if it were explicitly versioned and extended to express multiple possible endpoints. Possibly with different content/format/encoding.

Before we promote a v1.0 or coalesce repositories this is just a simple types change and a usage update, but afterwards it becomes vastly more complex and has a really burdened support expectation.

This issue is to write an RFC to get consensus about the approach, and #427 to implement the changes.

[grokspawn]

RFC completed review