Add config option to disable organisation creation for an DevGuard instance

[seb-kw]

Would be nice to have a env or something (configurable via Helm Chart) to disable further org creation for scenarios where admins want to only provide a single org on a instance.

[seb-kw]

https://gitlab.opencode.de/open-code/werkzeugkasten/helm-devguard/-/work_items/11