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/rum-src/regular-test.sh

@@ -0,0 +1,7 @@
+#!/bin/sh
+set -ex
+cd "$(dirname ${0})"
+dropdb --if-exist contrib_regression
+createdb contrib_regression
+PG_REGRESS=$(dirname "$(pg_config --pgxs)")/../test/regress/pg_regress
+${PG_REGRESS} --inputdir=./ --bindir='/usr/local/pgsql/bin' --use-existing --dbname=contrib_regression rum rum_hash ruminv timestamp orderby orderby_hash altorder altorder_hash limits int2 int4 int8 float4 float8 money oid time timetz date interval macaddr inet cidr text varchar char bytea bit varbit numeric rum_weight expr array