This means that services will only open their ports if they are
actually run, without having to clutter rules.v4 with a log of `if`
statements.
This does not go as far as using `puppetlabs/firewall`[1] because that
would represent an additional DSL to learn; raw IPtables sections can
easily be inserted into the generated iptables file via
`concat::fragment` (either inline, or as a separate file), but config
can be centralized next to the appropriate service.
[1] https://forge.puppet.com/modules/puppetlabs/firewall
This provides a single reference point for all zulip.conf settings;
these mostly link out to the more complete documentation about each
setting, elsewhere.
Fixes#12490.
Alex Vandiver
Anders Kaseorg