DependencyConvergence should support including/excluding certain dependencies

It would be nice if the DependencyConvergence rule could specify certain dependencies that should/should not fail the build. This might be useful if your project has a lot of dependency conflicts, but you know there are just a few troublesome ones that cause issues, and you don't want to resolve the conflicts for your entire project.

Here is my PR: https://github.com/apache/maven-enforcer/pull/136

Do I need to sign the Contributor License Agreement for this?