chore: upgrade PostgreSQL to 15

[davidgamez]

Summary:

This pull request upgrades the PostgreSQL version used in both the development and test environments, as well as in the Terraform-managed Google Cloud SQL instance, from version 14 to version 15. This ensures consistency across local and cloud environments and leverages the latest features and security updates.

PostgreSQL version upgrades:

• Updated the Docker image for the postgres service in docker-compose.yaml from postgis/postgis:14-3.3 to postgis/postgis:15-3.5.
• Updated the Docker image for the postgres-test service in docker-compose.yaml from postgis/postgis:14-3.3 to postgis/postgis:15-3.5.
• Changed the database_version for the Google Cloud SQL PostgreSQL instance in infra/postgresql/main.tf from POSTGRES_14 to POSTGRES_15.

Expected behavior:

Local Docker and deployed DB are upgraded to version 15.

Testing tips:

• Execute:

./scripts/docker-localdb-rebuild-data.sh 

• Verify that the local Docker DB has version 15 executing a sql command:

SELECT version()

Please make sure these boxes are checked before submitting your pull request - thanks!

• Run the unit tests with ./scripts/api-tests.sh to make sure you didn't break anything
• Add or update any needed documentation to the repo
• Format the title like "feat: [new feature short description]". Title must follow the Conventional Commit Specification(https://www.conventionalcommits.org/en/v1.0.0/).
• Linked all relevant issues
• Include screenshot(s) showing how this pull request works and fixes the issue(s)

[qcdyx]

LGTM