YARN-9630. [UI2] Add a link in docs's top page

Signed-off-by: Masatake Iwasaki <iwasakims@apache.org>
(cherry picked from commit eb6be4643f77b3284297950da4f7e6ca9db11793)

hadoop-project/src/site/site.xml

@@ -152,6 +152,7 @@
       <item name="Using GPU" href="hadoop-yarn/hadoop-yarn-site/UsingGpus.html"/>
       <item name="Using FPGA" href="hadoop-yarn/hadoop-yarn-site/UsingFPGA.html"/>
       <item name="Placement Constraints" href="hadoop-yarn/hadoop-yarn-site/PlacementConstraints.html"/>
+      <item name="YARN UI2" href="hadoop-yarn/hadoop-yarn-site/YarnUI2.html"/>
     </menu>
 
     <menu name="YARN REST APIs" inherit="top">

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/markdown/YarnUI2.md

@@ -43,7 +43,7 @@ origin (CORS) support.
 | `yarn.nodemanager.webapp.cross-origin.enabled` | true | Enable CORS support for Node Manager  |
 
 Also please ensure that CORS related configurations are enabled in `core-site.xml`.
-Kindly refer [here](https://hadoop.apache.org/docs/stable/hadoop-project-dist/hadoop-common/HttpAuthentication.html)
+Kindly refer [here](../../hadoop-project-dist/hadoop-common/HttpAuthentication.html)
 
 Use it
 -------------