Fix developer agent breaking when the default OLAP connector is invalid

[begelundmuller]

• Keeps the developer agent working even if the default OLAP connector is invalid or doesn't exist
• Adds an eval that tests if the developer agent can fix a misconfigured default OLAP connector

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. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!