HPCC-10775 Set job priority for multiple jobs in one ESP call

The existing code sets one job priority per ESP call. In the new
ECLWatch UI, multiple jobs may be selected to change job priority.
Multiple ESP calls have to be sent at the same time. After a few
successful calls, ESP stops to respond new calls.

In this fix, the code is added to support batch function which
allows to set job priority for multiple jobs in one ESP call.

This fix also depreciates two variables from SetJobPriority
request since they are not used.