Add regression tests for a cloud-based Neon instance (#8681)

## Problem
We need to be able to run the regression tests against a cloud-based
Neon staging instance to prepare the migration to the arm architecture.

## Summary of changes
Some tests were modified to work on the cloud instance (i.e. added
passwords, server-side copy changed to client-side, etc)

---------

Co-authored-by: Alexander Bayandin <[email protected]>

.github/workflows/cloud-regress.yml

@@ -0,0 +1,102 @@
+name: Cloud Regression Test
+on:
+  schedule:
+    # * is a special character in YAML so you have to quote this string
+    #          ┌───────────── minute (0 - 59)
+    #          │ ┌───────────── hour (0 - 23)
+    #          │ │ ┌───────────── day of the month (1 - 31)
+    #          │ │ │ ┌───────────── month (1 - 12 or JAN-DEC)
+    #          │ │ │ │ ┌───────────── day of the week (0 - 6 or SUN-SAT)
+    - cron:  '45 1 * * *' # run once a day, timezone is utc
+  workflow_dispatch: # adds ability to run this manually
+
+defaults:
+  run:
+    shell: bash -euxo pipefail {0}
+
+concurrency:
+  # Allow only one workflow
+  group: ${{ github.workflow }}
+  cancel-in-progress: true
+
+jobs:
+  regress:
+    env:
+      POSTGRES_DISTRIB_DIR: /tmp/neon/pg_install
+      DEFAULT_PG_VERSION: 16
+      TEST_OUTPUT: /tmp/test_output
+      BUILD_TYPE: remote
+      AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_DEV }}
+      AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_KEY_DEV }}
+
+    runs-on: us-east-2
+    container:
+      image: neondatabase/build-tools:pinned
+      options: --init
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: true
+
+      - name: Patch the test
+        run: |
+          cd "vendor/postgres-v${DEFAULT_PG_VERSION}"
+          patch -p1 < "../../patches/cloud_regress_pg${DEFAULT_PG_VERSION}.patch"
+
+      - name: Generate a random password
+        id: pwgen
+        run: |
+          set +x
+          DBPASS=$(dd if=/dev/random bs=48 count=1 2>/dev/null | base64)
+          echo "::add-mask::${DBPASS//\//}"
+          echo DBPASS="${DBPASS//\//}" >> "${GITHUB_OUTPUT}"
+
+      - name: Change tests according to the generated password
+        env:
+          DBPASS: ${{ steps.pwgen.outputs.DBPASS }}
+        run: |
+          cd vendor/postgres-v"${DEFAULT_PG_VERSION}"/src/test/regress
+          for fname in sql/*.sql expected/*.out; do
+            sed -i.bak s/NEON_PASSWORD_PLACEHOLDER/"'${DBPASS}'"/ "${fname}"
+          done
+          for ph in $(grep NEON_MD5_PLACEHOLDER expected/password.out | awk '{print $3;}' | sort | uniq); do
+            USER=$(echo "${ph}" | cut -c 22-)
+            MD5=md5$(echo -n "${DBPASS}${USER}" | md5sum | awk '{print $1;}')
+            sed -i.bak "s/${ph}/${MD5}/" expected/password.out
+          done
+
+      - name: Download Neon artifact
+        uses: ./.github/actions/download
+        with:
+          name: neon-${{ runner.os }}-${{ runner.arch }}-release-artifact
+          path: /tmp/neon/
+          prefix: latest
+
+      - name: Run the regression tests
+        uses: ./.github/actions/run-python-test-set
+        with:
+          build_type: ${{ env.BUILD_TYPE }}
+          test_selection: cloud_regress
+          pg_version: ${{ env.DEFAULT_PG_VERSION }}
+          extra_params: -m remote_cluster
+        env:
+          BENCHMARK_CONNSTR: ${{ secrets.PG_REGRESS_CONNSTR }}
+
+      - name: Create Allure report
+        id: create-allure-report
+        if: ${{ !cancelled() }}
+        uses: ./.github/actions/allure-report-generate
+
+      - name: Post to a Slack channel
+        if: ${{ github.event.schedule && failure() }}
+        uses: slackapi/slack-github-action@v1
+        with:
+          channel-id: "C033QLM5P7D" # on-call-staging-stream
+          slack-message: |
+            Periodic pg_regress on staging: ${{ job.status }}
+            <${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}|GitHub Run>
+            <${{ steps.create-allure-report.outputs.report-url }}|Allure report>
+        env:
+          SLACK_BOT_TOKEN: ${{ secrets.SLACK_BOT_TOKEN }}
+