HPCC-9935 Add SourceFormat to ESP FileSpray/SprayFixed request

In new ECLWatch UI, the SprayFixed Input page may add a Source
Format selection which contains: fixed, recfmv, recfmvb, and
variable. The FileSpray/SprayFixed should read the selection and
forward the selection to DFU workunit.

Signed-off-by: Kevin Wang <kevin.wang@lexisnexis.com>