Add two gitblit specific metrics for gc and ldap

Added metrics for:

1. git_garbage_collects_total
2. ldap_sync_latency_seconds.

Author: goettl79

src/main/java/com/gitblit/guice/WebModule.java

@@ -44,7 +44,10 @@
 import com.gitblit.servlet.SyndicationServlet;
 import com.gitblit.wicket.GitblitWicketFilter;
 import com.google.common.base.Joiner;
+import com.google.inject.Scopes;
 import com.google.inject.servlet.ServletModule;
+import io.prometheus.client.exporter.MetricsServlet;
+import io.prometheus.client.hotspot.DefaultExports;
 
 /**
  * Defines all the web servlets & filters.
@@ -79,6 +82,11 @@ protected void configureServlets() {
 		serve("/robots.txt").with(RobotsTxtServlet.class);
 		serve("/logo.png").with(LogoServlet.class);
 
+		// Prometheus
+		bind(MetricsServlet.class).in(Scopes.SINGLETON);
+		serve(fuzzy("/prometheus/")).with(MetricsServlet.class);
+		DefaultExports.initialize();
+
 		/* Prevent accidental access to 'resources' such as GitBlit java classes
 		 *
 		 * In the GO setup the JAR containing the application and the WAR injected