[#PIPE2D-712] Make 'init' block optional in generateCommands

generateCommands.py currently requires an init block in the YAML file. This makes sense for the integration test and weekly, but not for steady state processing. Make the init block optional.

(lsst-scipipe) pprice@tiger2-sumire:/scratch/pprice/pipe2d-709 $ generateCommands.py /projects/HSC/PFS/Subaru/ --calib /tigress/HSC/PFS/Subaru/CALIB-price --rerun price/pipe2d-709 --blocks=pipe2d_709 -j 20 pipe2d-709.yaml pipe2d-709.sh
Traceback (most recent call last):
  File "/tigress/HSC/PFS/stack/20190925/stack/miniconda3-4.5.12-1172c30/Linux64/pfs_pipe2d/w.2021.06a/bin/generateCommands.py", line 24, in <module>
    main()
  File "/tigress/HSC/PFS/stack/20190925/stack/miniconda3-4.5.12-1172c30/Linux64/pfs_pipe2d/w.2021.06a/python/pfs/pipe2d/generateCommands.py", line 94, in main
    return generateCommands(logger=logger, **vars(args))
  File "/tigress/HSC/PFS/stack/20190925/stack/miniconda3-4.5.12-1172c30/Linux64/pfs_pipe2d/w.2021.06a/python/pfs/pipe2d/generateCommands.py", line 1487, in generateCommands
    initSource, calibBlocks, scienceBlocks = processYaml(specFile)
  File "/tigress/HSC/PFS/stack/20190925/stack/miniconda3-4.5.12-1172c30/Linux64/pfs_pipe2d/w.2021.06a/python/pfs/pipe2d/generateCommands.py", line 1274, in processYaml
    initSource = InitSource.fromYaml(content["init"])
KeyError: 'init'

[PIPE2D-712] Make 'init' block optional in generateCommands Created: 13/Feb/21 Updated: 05/Mar/21 Resolved: 05/Mar/21
Status:	Won't Fix
Project:	DRP 2-D Pipeline
Component/s:	None
Affects Version/s:	None
Fix Version/s:	None

[PIPE2D-712] Make 'init' block optional in generateCommands Created: 13/Feb/21 Updated: 05/Mar/21 Resolved: 05/Mar/21