OLAP Connectors: Test the connection before exiting the "Add Data" modal

[ericpgreen2]

This PR ensures that a connection to the OLAP database is successfully established before finalizing the creation of a connector.yaml file and updating the .env file. Previously, submitting the ClickHouse, Druid, or Pinot connector forms would create these files regardless of the validity of the credentials.

Implementation details:

• Optimistically create a connector.yaml file.
• Optimistically create or update the .env file with the provided credentials.
• Call the OLAPListTables API to verify the connection.
• If the connection fails, remove the connector file, revert the changes made to the .env file, and display an error message.

Once #6671 lands, we can potentially switch the implementation to use a tmp directory and, in particular, a tmp/.env file to test credentials.

This PR builds on #6870, which should be reviewed first.

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated
• Intend to cherry-pick into the release branch
• I'm proud of this work!