Default to standalone DAG processor in breeze (apache#45723)

We are moving to only support a standalone DAG processor in Airflow 3,
so let's switch breeze to default to a standalone DAG processor, while
still allowing it to be explicitly disabled for Airflow 2.

Dockerfile.ci

@@ -1053,7 +1053,7 @@ function start_webserver_with_examples(){
     echo
     echo "${COLOR_BLUE}Parsing example dags${COLOR_RESET}"
     echo
-    airflow scheduler --num-runs 100
+    airflow dags reserialize
     echo "Example dags parsing finished"
     echo "Create admin user"
     airflow users create -u admin -p admin -f Thor -l Administrator -r Admin -e [email protected]

dev/breeze/doc/images/output_shell.txt

@@ -1 +1 @@
-1f9defd0443e2de2496b75a00c5af2cb
+d9370f833ddcc89db417a69b3de40a4b

dev/breeze/doc/images/output_start-airflow.txt

@@ -1 +1 @@
-e0c5377c9e26b5c5fa79b61ace516ea7
+a788bf6d34c4341a30287b60d134e43d

dev/breeze/src/airflow_breeze/commands/common_options.py

@@ -363,9 +363,11 @@ def _set_default_from_parent(ctx: click.core.Context, option: click.core.Option,
     envvar="SKIP_DB_TESTS",
 )
 option_standalone_dag_processor = click.option(
-    "--standalone-dag-processor",
-    help="Run standalone dag processor for start-airflow.",
+    "--standalone-dag-processor/--no-standalone-dag-processor",
     is_flag=True,
+    default=True,
+    show_default=True,
+    help="Run standalone dag processor for start-airflow (required for Airflow 3).",
     envvar="STANDALONE_DAG_PROCESSOR",
 )
 option_upgrade_boto = click.option(

scripts/docker/entrypoint_ci.sh

@@ -376,7 +376,7 @@ function start_webserver_with_examples(){
     echo
     echo "${COLOR_BLUE}Parsing example dags${COLOR_RESET}"
     echo
-    airflow scheduler --num-runs 100
+    airflow dags reserialize
     echo "Example dags parsing finished"
     echo "Create admin user"
     airflow users create -u admin -p admin -f Thor -l Administrator -r Admin -e [email protected]