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/pg_jsonschema-src/Makefile

@@ -1,8 +1,13 @@
 EXTENSION = pg_jsonschema
 DATA = pg_jsonschema--1.0.sql
 REGRESS = jsonschema_valid_api  jsonschema_edge_cases
-REGRESS_OPTS = --load-extension=pg_jsonschema
 
 PG_CONFIG ?= pg_config
 PGXS := $(shell $(PG_CONFIG) --pgxs)
-include $(PGXS)
+PG_REGRESS := $(dir $(PGXS))../../src/test/regress/pg_regress
+.PHONY installcheck:
+installcheck:
+	dropdb --if-exists contrib_regression
+	createdb contrib_regression
+	psql -d contrib_regression -c "CREATE EXTENSION $(EXTENSION)"
+	$(PG_REGRESS) --use-existing --dbname=contrib_regression $(REGRESS)