Replace a bunch of TODOs in the IANA Considerations

[yaronf]

Note that HTTP header fields are a unique science.

[jricher]

Wherever possible, please use HTTP Structured Fields as this will be brought up in the HTTP Directorate review. When structured fields are not possible, be clear about the ABNF rules. Most JOSE-encoded values use token68 as the production rule.

[bc-pi]

We've tried to give goodish ABNF at https://datatracker.ietf.org/doc/html/draft-ietf-wimse-s2s-protocol-03#section-4.1.1 and https://datatracker.ietf.org/doc/html/draft-ietf-wimse-s2s-protocol-03#section-4.2 knowing the appetite for HTTP Structured Fields and also that JWS doesn't fit particularly well into any of the SF items.

[yaronf]

Created a new issue #123 for the wimse URI scheme.