Add jar metadata with a link to this source code repository

[Sanne]

Today I wanted to experiment a quick patch in smallrye-common-vertx-context, which was in my application as a transitive dependency.

It's hard to find this repository and I had to ask around; it would be nice to have the repository links within the metadata of the jar: one can commonly find such links within the pom.xml or at least mentioned in the manifest.