Allow airgapped installation

[schulle877]

Summary

We like to use mailcow as our internal mailserver, having no contact to the outside world.
When installing I have no chance to set to deactivate rspamd to contact heinlein for example. The installation at that point.
Is it possible, or will it be possible to choose an airgapped installation.
PS: The docker images are proxied and I downloaded all needed scripts manually...

Motivation

Use mailcow as internal mailserver behind a firewall

Additional context

No response