Update the documentation of the cloud regress test (#11539)

## Problem
The information in the README.md contained errors, and some information
was missing.
## Summary of changes
Found errors are fixed, and new information is added.

---------

Co-authored-by: Alexander Bayandin <alexander@neon.tech>

test_runner/cloud_regress/README.md

@@ -3,19 +3,35 @@
 * 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:
+* Add the following settings to the `pg_settings` section of the default endpoint configuration for the project using the admin interface:
   * `Timeone`: `America/Los_Angeles`
   * `DateStyle`: `Postgres,MDY`
   * `compute_query_id`: `off`
+* Add the following section to the project configuration:
+```json
+"preload_libraries": {
+    "use_defaults": false,
+    "enabled_libraries": []
+  }
+```
 * 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 variables (please modify according your configuration):
+```bash
+$ export DEFAULT_PG_VERSION=17
+$ export BUILD_TYPE=release
+```
+* Build the Neon binaries see [README.md](../../README.md)
 * 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.
+* Update poetry, run
+```bash
+$ scripts/pysync
+```
 * Run 
 ```bash
-$ pytest -m remote_cluster -k cloud_regress
+$ scripts/pytest -m remote_cluster -k cloud_regress
 ```