More realistic PostgreSQL setup with dedicated users, database, and monitoring

- Replace the generic `root`/`otelu` users and `otel` database with a
  dedicated `astronomy_db` owned by `astronomy_user`, keeping the default
  `postgres` database untouched
- Add `monitoring_user` with `pg_monitor` role for read-only observability
  access across all databases and schemas
- Switch OTel Collector postgresql receiver to `monitoring_user` instead
  of the superuser
- Enable `pg_stat_statements` on all databases via
  `shared_preload_libraries` and `CREATE EXTENSION`
- Rename the Compose service and container from `postgresql` to
  `astronomy-db` for clarity; update `POSTGRES_HOST` accordingly
- Set `POSTGRES_PASSWORD` to `changeit` for the default superuser

Author: cyrille-leclerc

CHANGELOG.md

@@ -7,6 +7,12 @@ the release.
 
 ## Unreleased
 
+* [postgresql] More realistic PostgreSQL setup: replace generic `root`/`otelu` users
+  and `otel` database with dedicated `astronomy_db` owned by `astronomy_user`;
+  add `monitoring_user` with `pg_monitor` role for the OTel Collector receiver;
+  enable `pg_stat_statements` on all databases; rename Compose service and
+  container to `astronomy-db`
+  ([#3153](https://github.com/open-telemetry/opentelemetry-demo/pull/3153))
 * [accounting] fix memory leak with dbcontext
   ([#2876](https://github.com/open-telemetry/opentelemetry-demo/pull/2876))
 * [chore] Upgrade OTel Collector to v0.145.0 with :warning: breaking change: