nixos/doc: fix acme dns-01 example
nixos/doc: fix acme dns-01 example

Summary: fix errors with example code in the manual that shows how to set up DNS-01 verification via the acme protocol, e.g. for those who want to get wildcard certificates from Let's Encrypt.

Fix syntax error in nix arrays (there should not be commas.)

Fix permissions on /var/lib/secrets so it can be read by bind daemon. Without this fix bind won't start.

Add the missing feature: put the generated secret into certs.secret

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