ec2.py: Set source_dest_check default value to None (#42863)
ec2.py: Set source_dest_check default value to None (#42863)

* ec2.py:
  * source_dest_check default value is now None, updated docs
  * Refactor restart_instances and startstop_instances -> Two new functions to prevent repetition: check_source_dest_attr and check_termination_protection

thaim/ansible,thaim/ansible