RFC: link to Sonatype-hosted Scaladocs instead of javadoc.io?

We are in the midst of a 2-day+ javadoc.io outage, see https://github.com/maxcellent/javadoc.io/issues/180. This is not the first time unfortunately 😕

We currently use javadoc.io URLs by default both for inter-API linking and also on documentation websites.

However, because we are publishing our docs to Sonatype/Maven, they are also available at a Sonatype-hosted URL. For example:

https://s01.oss.sonatype.org/service/local/repositories/releases/archive/org/typelevel/cats-docs_2.13/2.10.0/cats-docs_2.13-2.10.0-javadoc.jar/!/index.html

We might consider switching to using the Sonatype URLs in all the places.

Pros:

• these URLs should be as permanent and live as Sonatype itself i.e. so long as our code artifacts are accessible there, the docs should be as well.

Cons:

• no fancy version picker
• it seems a bit slower (not to say javadoc.io can't be slow sometimes too).

Start by locating where sbt-typelevel constructs the default javadoc.io URLs for inter-API links and documentation websites. Compare those call sites with the Sonatype-hosted URL format in the issue, then determine the expected behavior for version navigation and confirm that generated links remain usable.