Devenv: Fix integration of postgres and fake-data-gen containers (#20329)

* Fix integration of postgres and fake-data-gen containers

This fix introduces the following modifications:
- Upgrades to 2.1 docker-compose file format
- Adds a health check for determining that postgrestest service is healthy
- Modifies the fake-postgres-data service to wait for postgrestest to be
"healthy" before starting.
- Renames postgrestest to postgres

devenv/docker/blocks/postgres/docker-compose.yaml

-  postgrestest:
+  postgres:
     image: postgres:${postgres_version}
     environment:
       POSTGRES_USER: grafana
@@ -7,6 +7,11 @@
     ports:
       - "5432:5432"
     command: postgres -c log_connections=on -c logging_collector=on -c log_destination=stderr -c log_directory=/var/log/postgresql
+    healthcheck:
+      test: [ "CMD", "pg_isready", "-q", "-d", "$$POSTGRES_DATABASE", "-U", "$$POSTGRES_USER" ]
+      timeout: 45s
+      interval: 10s
+      retries: 10
 
   fake-postgres-data:
     image: grafana/fake-data-gen
@@ -14,3 +19,6 @@
     environment:
       FD_DATASOURCE: postgres
       FD_PORT: 5432
+    depends_on:
+      postgres:
+        condition: service_healthy

devenv/docker/compose_header.yml

-version: "2"
+version: "2.1"
 services: