KAFKA-9519: Deprecate the --zookeeper flag in ConfigCommand (#8056)

Reviewers: Colin P. McCabe <cmccabe@apache.org>, Ron Dagostino <rndgstn@gmail.com>

core/src/main/scala/kafka/admin/ConfigCommand.scala

@@ -82,6 +82,8 @@ object ConfigCommand extends Config {
       opts.checkArgs()
 
       if (opts.options.has(opts.zkConnectOpt)) {
+        println(s"Warning: --zookeeper is deprecated and will be removed in a future version of Kafka.")
+        println(s"Use --bootstrap-server instead to specify a broker to connect to.")
         processCommandWithZk(opts.options.valueOf(opts.zkConnectOpt), opts)
       } else {
         processCommand(opts)
@@ -535,8 +537,8 @@ object ConfigCommand extends Config {
 
   class ConfigCommandOptions(args: Array[String]) extends CommandDefaultOptions(args) {
 
-    val zkConnectOpt = parser.accepts("zookeeper", "The connection string for the zookeeper connection in the form host:port. " +
+    val zkConnectOpt = parser.accepts("zookeeper", "DEPRECATED. The connection string for the zookeeper connection in the form host:port. " +
-            "Multiple URLS can be given to allow fail-over.")
+            "Multiple URLS can be given to allow fail-over. Replaced by --bootstrap-server, REQUIRED unless --bootstrap-server is given.")
             .withRequiredArg
             .describedAs("urls")
             .ofType(classOf[String])