spec!: add support for several topic matcher types, including URL Pattern

[dunglas]

Replaces #831 with a more flexible and future-proof approach.

Summary

• In addition to URI templates, regular expressions, URL patterns and CEL expressions are now supported
• the topic query parameter becomes match and now only supports exact matching
• new query parameters match{MatchType} are introduced
  • by default, matchRegexp, matchURLPattern, matchCEL, and matchURITemplate are defined
  • hub can implement custom matcher types
  • future updates may introduce new matcher types
• it's now possible to include per-topic (or topic matcher) payloads (replaces feat: payload for a specific topic #945)
• the JWT format has been updated to match these new capabilities
• the subscription API format has been updated to match these new capabilities

The official hub will be able to support both the current and new protocols simultaneously (no hard BC break).

TODO:

• update all examples