docs: ng-conf 2020 the musical (#34342)

Added event and announcement info for ng-conf 2020

PR Close #34342

aio/content/marketing/announcements.json

@@ -1,15 +1,15 @@
 [
   {
-    "startDate": "2019-04-02",
-    "endDate": "2019-04-20",
-    "message": "Join us for ng-conf<br/>May 1st-3rd, 2019",
+    "startDate": "2020-03-01",
+    "endDate": "2020-03-31",
+    "message": "Join us for ng-conf<br/>April 1st-3rd, 2020",
     "imageUrl": "generated/images/marketing/home/ng-conf.png",
-    "linkUrl": "http://ng-conf.org/?utm_source=angular.io&utm_medium=referral"
+    "linkUrl": "https://ng-conf.org/?utm_source=angular.io&utm_medium=referral"
   },
   {
-    "startDate": "2019-05-01",
-    "endDate": "2019-05-03",
-    "message": "Watch ng-conf live stream <br/>May 1st-3rd, 2019",
+    "startDate": "2020-04-01",
+    "endDate": "2020-04-03",
+    "message": "Watch ng-conf live stream <br/>April 1st-3rd, 2020",
     "imageUrl": "generated/images/marketing/home/ng-conf.png",
     "linkUrl": "https://www.ng-conf.org/livestream/?utm_source=angular.io&utm_medium=referral"
   },

aio/content/marketing/events.html

@@ -19,6 +19,12 @@
         <td>Delhi, India</td>
         <td>Feb 29, 2020</td>
       </tr>
+      <!-- ng-conf 2020 -->
+      <tr>
+        <th><a href="https://ng-conf.org/" title="ng-conf">ng-conf</a></th>
+        <td>Salt Lake City, Utah</td>
+        <td>April 1-3, 2020</td>
+      </tr>
     </tbody>
   </table>