Add better sample CIDRs for *_no_proxy parameters / use inventory-based approach

[berendt]

In most of our environments it's a bad idea to add 10.0.0.0/8,172.16.0.0/12,192.168.0.0/16 to the *_no_proxy parameters because all of the resource nodes are air-gapped by default. Rewrite https://osism.tech/docs/guides/configuration-guide/proxy to the inventory-based approach we use for REGIO.cloud. This makes most sense in the most scenarios.