refactor(gateway): remove responsiveness indicator

It doesn't yield much benefit over the existing health indicators for cluster and leader awareness.
It rather adds overhead requiring the user to configure the client additionally to the gateway itself.
General GRPC availability can be validated using the GRPC Health Probe instead.

(cherry picked from commit a0420be)

dist/src/main/resources/application-gateway.properties

@@ -6,6 +6,6 @@ management.endpoint.health.group.startup.include=gatewayStarted
 management.endpoint.health.group.startup.show-details=never
 management.endpoint.health.group.readiness.include=gatewayStarted
 management.endpoint.health.group.readiness.show-details=never
-management.endpoint.health.group.liveness.include=livenessGatewayResponsive,\
-  livenessGatewayClusterAwareness,livenessGatewayPartitionLeaderAwareness,livenessMemory
+management.endpoint.health.group.liveness.include=livenessGatewayClusterAwareness,\
+  livenessGatewayPartitionLeaderAwareness,livenessMemory
 management.endpoint.health.group.liveness.show-details=always

gateway/pom.xml

@@ -179,6 +179,12 @@
       <scope>test</scope>
     </dependency>
 
+    <dependency>
+      <groupId>io.camunda</groupId>
+      <artifactId>zeebe-client-java</artifactId>
+      <scope>test</scope>
+    </dependency>
+
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>
@@ -263,11 +269,6 @@
       <artifactId>spring-boot-actuator-autoconfigure</artifactId>
     </dependency>
 
-    <dependency>
-      <groupId>io.camunda</groupId>
-      <artifactId>zeebe-client-java</artifactId>
-    </dependency>
-
     <dependency>
       <groupId>io.netty</groupId>
       <artifactId>netty-transport</artifactId>

gateway/src/main/java/io/camunda/zeebe/gateway/impl/configuration/GatewayCfg.java

@@ -27,19 +27,13 @@ public class GatewayCfg {
   private SecurityCfg security = new SecurityCfg();
   private LongPollingCfg longPolling = new LongPollingCfg();
   private List<InterceptorCfg> interceptors = new ArrayList<>();
-  private boolean initialized = false;
 
   public void init() {
     init(ConfigurationDefaults.DEFAULT_HOST);
   }
 
   public void init(final String defaultHost) {
     network.init(defaultHost);
-    initialized = true;
-  }
-
-  public boolean isInitialized() {
-    return initialized;
   }
 
   public NetworkCfg getNetwork() {