Improve WebUI diagnosticMessage to show AM Container resource request size

When Yarn resources are insufficient, the newly submitted job AM may be in the state of "Application is Activated, waiting for resources to be assigned for AM". This is obviously because Yarn doesn't have enough resources to allocate another AM Container, so we want to know how large the AM Container is currently allocated. Unfortunately, the current diagnosticMessage on the Web page does not show this data. Therefore, it is necessary to add the resource size of the AM Container in the diagnosticMessage, which will be very useful for us to troubleshoise the production faults on line.