Installation signup and vendor list and contact info

[Ainali]

Is your feature request related to a problem? Please describe.
In case of security incidents or other urgent matters, it would be handy to know who is using OpenZaak and how to reach them.

Describe the solution you'd like
Some way to securely gather this information that also respects privacy. The information needs to be available to everyone in the Technical steering team. In the last technical steering meeting the task was assigned to @ericherman and me.

[Ainali]

This was discussed in the last technical steering team meeting where a draft was reviewed.