feat: New endpoint for shapefile data

[hepplerj]

This pull request introduces a new feature to handle and serve bills data with parish polygons in GeoJSON format. The primary changes include adding a new handler for this functionality, updating the routes to include the new endpoint, and providing example URLs for the new endpoint in the API documentation.

New feature implementation:

• bom-shapefiles.go: Added BillsShapefilesHandler to return a GeoJSON FeatureCollection containing parish polygons joined with bills data. This includes dynamic filtering and query execution with a timeout context for performance.
• bom-shapefiles.go: Introduced the buildSeparateFilters function to construct separate SQL filters for bills and parishes based on URL parameters.

Routing updates:

• routes.go: Added a new route /bom/bills-geometries to handle requests for bills data with parish polygons.

API documentation:

• endpoints.go: Updated the EndpointsHandler to include documentation and example URLs for the new /bom/bills-geometries endpoint.

Dependency additions:

• bom-shapefiles.go: Added imports for strings and time to support the new handler functionality.