- Finish interaction with Google Maps API through
src/googleMaps/mapsApi.ts.

- Now retrieving Shelter coordinates from Google Maps API everytime a
  new shelter is created or a already existent shelter is updated by
  admin.

- If API fetch is not working, it does not break the creation or update
  features.

- Loading Maps API key from .env file.

- Update env.example: Create MAPS_API_URL and MAPS_API_KEY variables.

Move the concern of retrieving the shelter coords from api and updating
payload, from controller to shelter.service

This commit refactors the shelter service by moving the logic for updating coordinates into a private method.
This eliminates repetitive code in both the store and fullUpdate methods.