Fixes #218

Supersedes #135

Based on work done davenverse/epimetheus#188 and is blocked by it (until it is merged and new version is published).

This contains mechanical changes needed to make the library compatible with Cats Effect 3.0 and Https4s 1.0.0-M20 (there might be more breaking changes in Http4s before release).

Noteworthy changes:

• support for OpenMetrics content output (this breaks API source and binary compatibility, because old 004 related methods have new names - no fallback provided)
• Sync is relaxed from routes creation as defining routes should not be really effectful, so, only needed typeclasses from cats are used (running the routes is effectful indeed, but then Sync will be supplied to it in the calling code).
• added methods from Support for using collection of registries in Scraper #135 to allow using multiple collectors. There was a discussion, that it sometimes defining/using multiple Collectors could throw exceptions, but I think it is acceptable to have these methods and just accept this fact as implementation detail from the library used. Custom exporters registered inside Collectors could throw exceptions being polled as well and we just accept that fact.

Making this as Draft, because it is blocked by PR in epimetheus repo.