TMSS-585: Add scheduling state model and referencing field to project model

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

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

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

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