report the externally discovered reproducers

[tarasmadan]

Is your feature request related to a problem? Please describe.
External researchers upstream their findings directly to upstream.
Upstream developers often feel more comfortable working with the syzbot reported findings.

Describe the solution you'd like
We can let external researchers to upstream their findings using syzbot. The first version may be the form to submit the reproducer.
Syzbot will check its correctness and upstream with "reported-by: [email protected]".
The improved version may allow to submit some reproducer + additional descriptions.