Support Gradle 6 version alignment with Jackson Scala module (`jackson-module-scala`)

(as background, see https://github.com/FasterXML/jackson-databind/issues/2726)

So, Jackson 2.12 is adding support for Gradle version alignment, using mechanism supported by Gradle 6.
@jjohannes contributed this for other modules and hopefully can help, or at least indicate whether this is feasible with `sbt` build. There may also be changes needed to `jackson-integration-tests` test repo, depending on whether metadata may be added.