TMSS-166: Rework on review comments

SAS/TMSS/src/tmss/tmssapp/populate.py

SAS/TMSS/src/tmss/tmssapp/schemas/CMakeLists.txt

SAS/TMSS/src/tmss/tmssapp/schemas/empty-schema.json

SAS/TMSS/src/tmss/tmssapp/schemas/scheduling-unit.json

...src/tmss/tmssapp/schemas/subtask-observation-control.json

...SS/src/tmss/tmssapp/schemas/subtask-pipeline-control.json

SAS/TMSS/src/tmss/tmssapp/schemas/subtask-qa-files.json

SAS/TMSS/src/tmss/tmssapp/schemas/subtask-qa-plots.json

SAS/TMSS/src/tmss/tmssapp/schemas/task-calibrator-addon.json

.../tmss/tmssapp/schemas/task-observation-with-stations.json

SAS/TMSS/src/tmss/tmssapp/schemas/task-relation-sap.json

SAS/TMSS/src/tmss/tmssapp/tasks.py

SAS/TMSS/src/tmss/tmssapp/viewsets/specification.py

SAS/TMSS/test/CMakeLists.txt

SAS/TMSS/test/t_tasks.py

SAS/TMSS/test/testdata/example_UC1_scheduling_unit.json