Minor error in the monitoring docs. Also made indentation changes in `ApiRootResource`

Author: Hari Shreedharan <hshreedharan@apache.org>

Closes #6628 from harishreedharan/eventlog-formatting and squashes the following commits:

a12553d [Hari Shreedharan] Javadoc updates.
ca399b6 [Hari Shreedharan] [HOTFIX] History Server API docs error fix.