feat: Add an option to get hits by user agent in analytics dashboard

This closes gravitee-io/issues#1951

src/main/java/io/gravitee/reporter/api/http/Metrics.java

@@ -49,6 +49,7 @@ public final class Metrics extends AbstractMetrics {
     private Log log;
     private String path;
     private String mappedPath;
+    private String userAgent;
 
     private Metrics(long timestamp) {
         super(timestamp);
@@ -238,6 +239,14 @@ public void setHost(String host) {
         this.host = host;
     }
 
+    public String getUserAgent() {
+        return userAgent;
+    }
+
+    public void setUserAgent(String userAgent) {
+        this.userAgent = userAgent;
+    }
+
     public static Builder on(long timestamp) {
         return new Builder(timestamp);
     }