Add EC2 start / stop functions for use in public & genie dags

[jamesqo]

/cc @sheridancbio @averyniceday

• Add turn_ec2_on and turn_ec2_off tasks that use EC2Start/StopInstanceOperator to control the KS node directly from the Airflow server
  • Approach: use saml2aws (installed on the Airflow server) to dynamically generate a new Airflow AWS connection based on the SAML credentials. Then, pass to the EC2 operators via aws_conn_id
• Only shut down the ec2 node if it is determined that there are no active imports running
  • Go into the importer mgmt database on Clickhouse and check the status for each of the relevant portals -- in this case, public and genie
  • Decided to implement this using Airflow metadata DB -- check if import_genie_dag is running from the public DAG, and vice versa