Documentation Helidon MP: Update several guides for minor issues (#2616)

* Remove GreetApplication from metrics guide

Signed-off-by: tvallin <thibault.vallin@oracle.com>

* Fix metrics guide

Signed-off-by: tvallin <thibault.vallin@oracle.com>

* Fix config guide

Signed-off-by: tvallin <thibault.vallin@oracle.com>

docs/mp/guides/03_config.adoc

@@ -84,6 +84,41 @@ system properties, environment variables, and  the contents of `META-INF/micropr
 For example, if you specify a custom server port in `META-INF/microprofile-config.properties`
 then your server will listen on that port.
 
+A main class is also required to start up the server and run the
+application. If you don't use Helidon's built-in main class you can
+define your own:
+
+[source,java]
+.src/main/java/io/helidon/examples/quickstart/mp/Main.java
+----
+package io.helidon.examples.quickstart.mp;
+
+import io.helidon.microprofile.server.Server;
+import java.io.IOException;
+
+public final class Main {
+
+    private Main() { } // <1>
+
+    public static void main(final String[] args) throws IOException {
+        Server server = startServer();
+        System.out.println("http://localhost:" + server.port() + "/greet");
+    }
+
+    static Server startServer() {
+        return Server.create().start(); // <2>
+    }
+
+}
+----
+In this class, a `main` method is defined which starts the Helidon MP
+server and prints out a message with the listen address.
+
+<1> Notice that
+this class has an empty no-args constructor to make sure this class
+cannot be instantiated.
+<2> The MicroProfile server is started with the default configuration.
+
 In your application code, Helidon uses the default configuration when you create a `Server` object without a custom `Config` object.
 See the following code from the project you created.
 

docs/mp/guides/05_metrics.adoc

@@ -140,14 +140,6 @@ curl -H "Accept: application/json"  http://localhost:8080/metrics
     "thread.max.count": 44
   },
   "vendor": {
-    "grpc.requests.count": 0,
-    "grpc.requests.meter": {
-      "count": 0,
-      "meanRate": 0.0,
-      "oneMinRate": 0.0,
-      "fiveMinRate": 0.0,
-      "fifteenMinRate": 0.0
-    },
     "requests.count": 6,
     "requests.meter": {
       "count": 6,
@@ -163,26 +155,26 @@ curl -H "Accept: application/json"  http://localhost:8080/metrics
 You can get a single metric by specifying the name in the URL path.
 
 [source,bash]
-.Get the Helidon `grpc.requests.meter` metric:
+.Get the Helidon `requests.meter` metric:
 ----
-curl -H "Accept: application/json"  http://localhost:8080/metrics/vendor/grpc.requests.meter
+curl -H "Accept: application/json"  http://localhost:8080/metrics/vendor/requests.meter
 ----
 
 [source,json]
 .JSON response:
 ----
 {
-  "grpc.requests.meter": {
-    "count": 0,
-    "meanRate": 0.0,
-    "oneMinRate": 0.0,
-    "fiveMinRate": 0.0,
-    "fifteenMinRate": 0.0
+  "requests.meter": {
+    "count": 6,
+    "meanRate": 0.008275992296704147,
+    "oneMinRate": 0.01576418632772332,
+    "fiveMinRate": 0.006695060022357365,
+    "fifteenMinRate": 0.0036382699664488415
   }
 }
 ----
 
-NOTE: You cannot get the individual fields of a metric. For example, you cannot target http://localhost:8080/metrics/vendor/grpc.requests.meter.count.
+NOTE: You cannot get the individual fields of a metric. For example, you cannot target http://localhost:8080/metrics/vendor/requests.meter.count.
 
 ==== Controlling `REST.request` metrics
 Helidon implements the optional family of metrics, all with the name `REST.request`, as described in the
@@ -311,17 +303,6 @@ The default behavior is to decrement when exiting the method.  Here is an exampl
 `@Counted(name = "any-card", monotonic = true)`.
 
 
-[source,java]
-.Update the `GreetApplication` class as follows:
-----
-@Override
-public Set<Class<?>> getClasses() {
-    return Set.of(GreetResource.class, GreetingCards.class); // <1>
-}
-----
-<1> Add the `GreetingCards` class to the set of classes managed by Helidon for this application.
-
-
 [source,bash]
 .Build and run the application, then invoke the application endpoints below:
 ----