TMSS-682: Create ReservationStrategyTemplate stating with a simple core maintenance strategy

SAS/TMSS/backend/src/tmss/tmssapp/migrations/0001_initial.py

SAS/TMSS/backend/src/tmss/tmssapp/models/specification.py

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

...pp/schemas/simple-core-stations-reservation-strategy.json

SAS/TMSS/backend/src/tmss/tmssapp/schemas/templates.json

...MSS/backend/src/tmss/tmssapp/serializers/specification.py

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

SAS/TMSS/backend/src/tmss/urls.py

SAS/TMSS/backend/test/tmss_test_data_django_models.py

SAS/TMSS/client/lib/populate.py