[BUG] udf-examples dependencies are incorrect

[jlowe]

The udf-examples subproject depends on the unpublished rapids-4-spark-sql rather than the published distribution jar, rapids-4-spark. Simply updating the dependency to be what is expected will break the test build phase as described in #3966.

Ideally the UDF examples project should be migrated to an external project repository so it more accurately reflects a true example that users can replicate and is not involved in the build process of the RAPIDS Accelerator directly. By building the examples in the same repository as the RAPIDS Accelerator, we risk accidentally relying on an environment that an external project cannot replicate without also building the RAPIDS Accelerator.