Run the extensions' tests on staging (#11164)

## Problem
We currently don't run end-to-end tests for PostgreSQL extensions on our
cloud infrastructure, which means we might miss problems that only occur
in a real cloud environment.

## Summary of changes
- Added a workflow to run extension tests against a cloud staging
instance
- Set up proper project configuration for extension testing
- Implemented test execution with appropriate environment settings
- Added error handling and reporting for test failures

---------

Co-authored-by: Alexander Bayandin <alexander@neon.tech>
Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

docker-compose/ext-src/pgjwt-src/neon-test.sh

@@ -1,4 +1,6 @@
 #!/bin/bash
 set -ex
 cd "$(dirname "${0}")"
-pg_prove test.sql
+dropdb --if-exists contrib_regression
+createdb contrib_regression
+pg_prove -d contrib_regression test.sql