Create model tables for census tracts

[pratishta]

Similar to #130

Acceptance criteria

• Create a branch for zoning-api, write the census-tract.ts schema file with schemas for census tracts. Run migrations and ensure the tables look as expected in the DB
• Create census-tracts.sh and census-tracts.sql under db/pg/model-create, get the schema dump from the tables just created in zoning-api, ensure model tables have been created in data-flow DB