Support Serialized DAGs on CLI Commands

**Description**

CLI commands such as backfill and list_dags currently parse dags before executing. This introduces 2 primary issues. 1) That parse process can be time consuming, and 2) It will not work if running on a web server that does not have access to DAGs and/or their respective Python libraries or Airflow plugins.

**Use case / motivation**

By providing users an option to use serialized DAGs with the Airflow CLI, users can opt for the more efficient method of executing commands based on the information available in the metadatabase rather than relying solely on parsing the source DAGs.

**Are you willing to submit a PR?**

Yes

**Related Issues**

No