MAPREDUCE-7246. In MapredAppMasterRest#Mapreduce_Application_Master_Info_API, updating the datatype of appId to "string". (#4223)

Co-authored-by: Ashutosh Gupta <ashugpt@amazon.com>
Signed-off-by: Akira Ajisaka <aajisaka@apache.org>

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/site/markdown/MapredAppMasterRest.md

@@ -48,7 +48,7 @@ When you make a request for the mapreduce application master information, the in
 
 | Item | Data Type | Description |
 |:---- |:---- |:---- |
-| appId | long | The application id |
+| appId | string | The application id |
 | startedOn | long | The time the application started (in ms since epoch) |
 | name | string | The name of the application |
 | user | string | The user name of the user who started the application |