Describe the bug

flakes is ok to configure on the client only.
ca-derivations and uid allocation must be set in the system configuration (if applicable)

Steps To Reproduce

Read the manual. Encounter an experimental feature setting hint.
https://nixos.org/manual/nix/stable/command-ref/conf-file.html?highlight=nix.conf#conf-auto-allocate-uids

Warning This is an experimental feature.

To enable it, add the following to nix.conf:

extra-experimental-features = auto-allocate-uids
auto-allocate-uids = true

Which nix.conf?

Expected behavior

A clear and concise description of what you expected to happen.

nix-env --version output

Additional context

Debt found while reviewing #8196

Priorities

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