Specify how delegated /routing/v1 API can support new protocols

[lidel]

Extracted loose ends from IPIP-337 (to unblock it), but we need to address below at some point.
cc @guseggert @aschmahmann @masih

Open questions

• How do we deal with plain text labels from table.csv changing in the future?
  • It happened before: go-cid had invalid mapping, and we changed label for at least 4 codes
  • Can we allow numeric values instead (indicate them in hex, start with 0x)
• How do we allow for novel protocols that do not have multicodec registered?
  • https://github.com/ipfs/specs/pull/337/files#r1044055388
• How does the use of Schema interact with systems like IPNI?
  • https://github.com/ipfs/specs/pull/337/files#r1044060034

Maybe more tangible example:

• How does Iroh announce their blake3-specific data transfer protocol?

Idea 1

• Protocol is the multicodec name of the transfer protocol or an opaque string
  • for protocols with multicodec, a numeric code starting with 0x can be used instead of name
  • for protocols without multicodec registered, we could go with UUID in hex form (also 0x prefix, but we avoid collisions due to them bveing long enough)

Idea 2

• state Protocol and Schema are opaque strings, and write convention how to return opaque records as base-encoded bytes.
  • there is some conceptual ovelap with Propose Naam as naming system powered by IPNI ipni/specs#4