feat: task instances and logs from airflow

[helen-m-lin]

closes #127

• Add /api/v1/get_tasks_list for getting airflow tasks, given the dag_run_id
• Add /api/v1/get_task_logs for getting logs, given the dag_run_id, task_id, and try_number
• Add Jinja templates for displaying tasks results and logs results. These are used as iframes within job status or tasks tables
  • User can click the "View tasks and logs" button for any job to see a list of associated tasks for that job
  • User can click the "View logs" button for any task instance (with valid try_number) to see its logs.

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New tasks buttons:

New Tasks popup with logs buttons:

New Logs popup for each task: