Enforce integer processing versions

This extends the support in WMWorkload and WMTask to include a
processing string along with the processing version and acquisition era.
The processing version is now enforced to be an integer and the lfns are built as following:

<acquisitionEra>-<processingString>-v<processingVersion>

The job reports contain all these three elements for each output file
however the DBSBuffer will only use the processing version and acquisition era.

The ReqMgr changes to allow the specification of these parameters in the assign page,
also updated the tests and templates. Include a test template for TaskChain with multiple
tasks, multiple acquisition eras and versions.

Fixes #4007