Release notes contain link to new Javadoc

[mstachniuk]

When "org.shipkit.javadoc" plugin is applied, then release notes should contain a link (as a badge) to the published Javadoc.

By default, the link should point to the specified directory ("javadoc.repositoryDirectory") and branch "javadoc.repositoryBranch" (see ShipkitConfiguration.java for more configuration options).

There should be also a possibility to point to some class, e.g. for Mockito project link can point to the "org.mockito.Mockito" class. This should be configurable.

Starting point: https://github.com/mockito/shipkit/blob/4b65fe696f2fae7be07e3db77bda91be2299c217/subprojects/shipkit/src/main/groovy/org/shipkit/internal/gradle/notes/tasks/UpdateReleaseNotes.java#L97-L101