feat(ui): add source links in the alert action menu

ui/src/Components/Grid/AlertGrid/AlertGroup/Alert/AlertMenu.js

@@ -42,6 +42,19 @@ const MenuContent = onClickOutside(
         >
           <FontAwesomeIcon icon={faBellSlash} /> Silence this alert
         </div>
+        <h6 className="dropdown-header">Alert source links:</h6>
+        {alert.alertmanager.map(am => (
+          <a
+            key={am.name}
+            className="dropdown-item"
+            href={am.source}
+            target="_blank"
+            rel="noopener noreferrer"
+            onClick={afterClick}
+          >
+            {am.name}
+          </a>
+        ))}
       </div>
     );
   }

ui/src/Components/Grid/AlertGrid/AlertGroup/Alert/AlertMenu.test.js

@@ -74,4 +74,10 @@ describe("<MenuContent />", () => {
     button.simulate("click");
     expect(silenceFormStore.toggle.visible).toBe(true);
   });
+
+  it("source link points at alert source", () => {
+    const tree = MountedMenuContent(group);
+    const link = tree.find("a.dropdown-item[href='localhost/prometheus']");
+    expect(link.text()).toBe("default");
+  });
 });