Register `monetization` Link Relation

Registered Link Relation types are recorded by the IETF at https://www.iana.org/assignments/link-relations/link-relations.xhtml

RFC 8288 defined the process for registering. There is now an updated GitHub workflow.

I believe Web Monetization fulfills the requirements for stability, both as an open source project in a community organization and as a specification incubating in the W3C WICG.

• "Specification required"
• Clarified: "Suitable Specification References. This registry requires a stable reference for a specification document. Publication by a recognised open standards body is preferred; however, publication by established Open Source projects (i.e., those that demonstrate a community that's committed to ongoing support), community and commercial organizations are also accepted, provided that they have a reasonable plan to promote specification stability."
• "When to register: Generally, a registration request should be made when your document is mature enough for wide review. If your reference is an Internet-Draft, that means when it's adopted by a stream (e.g., the IETF stream, the Independent stream), not beforehand. If your reference is in another standards body, a request can be made before the document is finalised."

Even if the registration were to not be deemed premature, having a public registration request pending establishes our intent to use the monetization name.

• "For the First Come First Served policy, assignments are made to anyone on a first come, first served basis. There is no substantive review of the request, other than to ensure that it is well-formed and doesn't duplicate an existing assignment."

Alternative option: HTML Living Standard (managed by WHATWG, no longer by W3C) suggests using the Microformats process for registering rel values, but also recognizes IETF RFCs:

Start with RFC 8288 and the updated protocol-registries/link-relations registration workflow linked in the issue, then review the Web Monetization specification's maturity and the alternative HTML Living Standard and Microformats processes. Done means the monetization link relation has an appropriate public registration request or an agreed registration path.