Return NotSupported in scan if IOUring not supported and enable IOUring in db_stress for async_io testing (#11197)

Summary:
- Return NotSupported in scan if IOUring not supported if async_io is enabled
- Enable IOUring in db_stress for async_io testing
- Disable async_io in circleci crash testing as circleci doesn't support IOUring

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11197

Test Plan: CircleCI jobs

Reviewed By: anand1976

Differential Revision: D43096313

Pulled By: akankshamahajan15

fbshipit-source-id: c2c53a87636950c0243038b9f5bd0d91608e4fda