Improve health check

[iwysiu]

What happened:
Saving an incorrect Redshift config and the health check still returns a Data source is working message. However, as you would expect, actually running a query with the configured datasource fails.

What you expected to happen:
CheckHealth should be implemented with a simple query (maybe fetching clusters, see if that works with the secrets manager) to make sure we can actually query with the saved config.

How to reproduce it (as minimally and precisely as possible):
Save a datasource with an invalid Access and Secret Key pair, and you should observe that it saves with a Data source is working message. Then try to create a query with that datasource and it should fail.

[github-actions]

This issue has been automatically marked as stale because it has not had activity in the last year. It will be closed in 30 days if no further activity occurs. Please feel free to leave a comment if you believe the issue is still relevant. Thank you for your contributions!