Add log message in release.py (#8461)

When building a release candidate with release.py, if it's not the first RC, we need to drop the previous RC's artifacts from the staging repository before closing the new ones. This adds a log message to remind the release manager of this

release.py

@@ -688,6 +688,8 @@ if not user_ok("Have you sufficiently verified the release artifacts (y/n)?: "):
 print("Next, we need to get the Maven artifacts we published into the staging repository.")
 # TODO: Can we get this closed via a REST API since we already need to collect credentials for this repo?
 print("Go to https://repository.apache.org/#stagingRepositories and hit 'Close' for the new repository that was created by uploading artifacts.")
+print("If this is not the first RC, you need to 'Drop' the previous artifacts.")
+print("Confirm the correct artifacts are visible at https://repository.apache.org/content/groups/staging/org/apache/kafka/")
 if not user_ok("Have you successfully deployed the artifacts (y/n)?: "):
     fail("Ok, giving up")
 if not user_ok("Ok to push RC tag %s (y/n)?: " % rc_tag):