Implemeted extend schema decorator to document the error response for /databases/ endpoint

[varshadr]

Fixes #3068

This pull request introduces the Extend Schema decorator to the DatabasesViewSet. By utilizing the decorator, we will document the missing 404 error response for /api/ui/v0/databases/{id}/types/, that DRF spectacular failed to document.

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[github-actions]

This pull request has not been updated in 45 days and is being marked as stale. It will automatically be closed in 30 days if not updated by then.

[mathemancer]

We're reprioritizing, and unfortunately, we can't continue the documentation project.