Enable the pg_regress tests on staging for PG17 (#9978)

## Problem
Currently, we run the `pg_regress` tests only for PG16
However, PG17 is a part of Neon and should be tested as well 
## Summary of changes
Modified the workflow and added a patch for PG17 enabling the
`pg_regress` tests.
The problem with leftovers was solved by using branches.

test_runner/cloud_regress/README.md

@@ -0,0 +1,21 @@
+# How to run the `pg_regress` tests on a cloud Neon instance.
+
+* Create a Neon project on staging.
+* Grant the superuser privileges to the DB user.
+* (Optional) create a branch for testing
+* Configure the endpoint by updating the control-plane database with the following settings:
+  * `Timeone`: `America/Los_Angeles`
+  * `DateStyle`: `Postgres,MDY`
+  * `compute_query_id`: `off`
+* Checkout the actual `Neon` sources
+* Patch the sql and expected files for the specific PostgreSQL version, e.g. for v17:
+```bash
+$ cd vendor/postgres-v17
+$ patch -p1 <../../compute/patches/cloud_regress_pg17.patch
+```
+* Set the environment variable `BENCHMARK_CONNSTR` to the connection URI of your project.
+* Set the environment variable `PG_VERSION` to the version of your project.
+* Run 
+```bash
+$ pytest -m remote_cluster -k cloud_regress
+```

test_runner/cloud_regress/test_cloud_regress.py

@@ -5,68 +5,15 @@ Run the regression tests on the cloud instance of Neon
 from __future__ import annotations
 
 from pathlib import Path
-from typing import Any
 
-import psycopg2
 import pytest
-from fixtures.log_helper import log
 from fixtures.neon_fixtures import RemotePostgres
 from fixtures.pg_version import PgVersion
 
 
-@pytest.fixture
-def setup(remote_pg: RemotePostgres):
-    """
-    Setup and teardown of the tests
-    """
-    with psycopg2.connect(remote_pg.connstr()) as conn:
-        with conn.cursor() as cur:
-            log.info("Creating the extension")
-            cur.execute("CREATE EXTENSION IF NOT EXISTS regress_so")
-            conn.commit()
-            # TODO: Migrate to branches and remove this code
-            log.info("Looking for subscriptions in the regress database")
-            cur.execute(
-                "SELECT subname FROM pg_catalog.pg_subscription WHERE "
-                "subdbid = (SELECT oid FROM pg_catalog.pg_database WHERE datname='regression');"
-            )
-            if cur.rowcount > 0:
-                with psycopg2.connect(
-                    dbname="regression",
-                    host=remote_pg.default_options["host"],
-                    user=remote_pg.default_options["user"],
-                    password=remote_pg.default_options["password"],
-                ) as regress_conn:
-                    with regress_conn.cursor() as regress_cur:
-                        for sub in cur:
-                            regress_cur.execute(f"ALTER SUBSCRIPTION {sub[0]} DISABLE")
-                            regress_cur.execute(
-                                f"ALTER SUBSCRIPTION {sub[0]} SET (slot_name = NONE)"
-                            )
-                            regress_cur.execute(f"DROP SUBSCRIPTION {sub[0]}")
-                        regress_conn.commit()
-
-    yield
-    # TODO: Migrate to branches and remove this code
-    log.info("Looking for extra roles...")
-    with psycopg2.connect(remote_pg.connstr()) as conn:
-        with conn.cursor() as cur:
-            cur.execute(
-                "SELECT rolname FROM pg_catalog.pg_roles WHERE oid > 16384 AND rolname <> 'neondb_owner'"
-            )
-            roles: list[Any] = []
-            for role in cur:
-                log.info("Role found: %s", role[0])
-                roles.append(role[0])
-            for role in roles:
-                cur.execute(f"DROP ROLE {role}")
-            conn.commit()
-
-
 @pytest.mark.timeout(7200)
 @pytest.mark.remote_cluster
 def test_cloud_regress(
-    setup,
     remote_pg: RemotePostgres,
     pg_version: PgVersion,
     pg_distrib_dir: Path,