[lve-tools, web] Enable private disclosure of very sensitive LVEs

[lbeurerkellner]

To enable the disclosure of LVEs that are too sensitive to be hosted publicly, we want to provide an upload form that allows to disclose sensitive LVEs. The core team can then reproduce and confirm such LVEs, and provide an abstract description publicly, as part of the repository. On request, model vendors may then request the sensitive payloads to fix the issues with their models if possible.