Preserve existing outputs patch

See PR: https://github.com/microsoft/onefuzz/pull/1739 for Python version of the code. 

The PR needs to be ported to C#

[AB#36101](https://fuzzfest.visualstudio.com/5eaacf23-2084-4d62-8fbe-7d37326a8b74/_workitems/edit/36101)