TMSS-308: Change SAPs to be named in schemas, change handling accordingly, fix/add tests

SAS/TMSS/src/tmss/tmssapp/models/scheduling.py

...app/schemas/UC1-scheduling-unit-observation-strategy.json

...pp/schemas/dataproduct_specifications_template-SAP-1.json

.../tmss/tmssapp/schemas/subtask_template-observation-1.json

...src/tmss/tmssapp/schemas/subtask_template-pipeline-1.json

...ssapp/schemas/task_relation_selection_template-SAP-1.json

...ssapp/schemas/task_template-calibrator_observation-1.json

...s/tmssapp/schemas/task_template-target_observation-1.json

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

SAS/TMSS/test/t_scheduling.py

SAS/TMSS/test/t_subtasks.py

SAS/TMSS/test/t_tmssapp_scheduling_django_API.py

SAS/TMSS/test/testdata/example_UC1_scheduling_unit.json