AIP-38 | New Dashboard homepage

[bbovenzi]

Create a new homepage dashboard to give an overview of what is happening on the airflow deployment. Essentially, migrate and expand upon Cluster Activity

• Add a new Dashboard page
• Show cluster health stats
• AIP-38 | Show historic metrics in Dashboard #42700
• Show pool slot stats
• Show DAG import errors
• Quick links to DAGs with failed runs or running runs
• Add an event timeline to help with date range selection

[raphaelauv]

in Show cluster health stats

it would be very nice to also show the number of components ( scheduler(s) , celery-worker(s) , triggerer(s) , dag-processor(s) )