[AIRFLOW-2814] Fix inconsistent default config

value of min_file_process_interval in config
template is 0
However it's supposed to be 180 according to
airflow/jobs.py line 592

Closes #3659 from XD-DENG/patch-3

airflow/config_templates/default_airflow.cfg

@@ -428,8 +428,8 @@ scheduler_heartbeat_sec = 5
 # -1 indicates to run continuously (see also num_runs)
 run_duration = -1
 
-# after how much time a new DAGs should be picked up from the filesystem
-min_file_process_interval = 0
+# after how much time (seconds) a new DAGs should be picked up from the filesystem
+min_file_process_interval = 180
 
 # How many seconds to wait between file-parsing loops to prevent the logs from being spammed.
 min_file_parsing_loop_time = 1