Introduce a new database schema

We are creating a new database schema:

• using schemas instead of different databases
• including all data sources
• Created tables: sources, entities, taxonomies, assets, metadata, baseline_assets, district_assets
• Added primary and foreign key constraints
• Defined unique and partial indexes for optimized queries
• Needed functions:
  • upsert_tile(): Adds a tile entity if it does not exist
  • calculate_completeness(): Computes completeness of a tile based on built area
  • update_completeness(): Updates completeness of intersecting tiles
  • update_tile(): Executes upsert and completeness updates via a trigger
• Created trigger_update_tile to automatically update tile completeness on entity insert/update
• Created tables under sources schema:
  • google_buildings: Stores Google building footprints with confidence scores
  • microsoft_buildings: Stores Microsoft building footprints with height and quadkey reference
  • boundaries: Stores geographical boundary data
  • ghsl_characteristics: Stores GHSL-based characteristics
• Added indexes for spatial queries:
  • GIST indexes on geometry columns for efficient geospatial lookups
  • Index on plus_code in google_buildings