Allow marking files as sources JARs for use in Maven

[BasiqueEvangelist]

Right now, the only special cased artifact in maven is the main artifact, which is aliased to the primary file of the version. This makes it easy to use mods through the maven, even if the author didn't specifically add support. However, using other classifiers (for example, sources) requires naming the version file the way Maven expects it to be named. (I think the docs aren't even entirely correct here, as sources jars need to specifically be artifactid-version-sources.jar)

Not only is this rather confusing (as some threads in #website-support can attest), this is also rather brittle: if the project's slug changes, or the version is referenced in a different way, the maven will stop serving it under the correct path and sources won't be linked.

Proposed solution

Modrinth has a file type system, which is currently used for providing required/optional resource packs together with data packs. Adding a 'Sources' file type that the maven aliases to the correct sources path (and possibly even adding support for autopublishing sources jars from Minotaur) would make it much easier to provide sources on the Maven.
A special javadoc file type would also be a nice addition, although I don't think it's as useful as sources for developing against mods.

[dphaldes]

This problem can be seen in the project file https://modrinth.com/mod/blood-magic/version/3.3.2-44.
The jar name is "bloodmagic-1.20.1-3.3.2-44-sources.jar" and because it is not in the same format as Maven expects it, the sources are not fetched