Fixes #24057 - Email subject prefix accepts long strings (#5742)

Fixes #23635 - Centralize use of facter

We have a bundler group for facter. That implies it's optional but
before this change it wasn't With this change it's only required if no
domain and fqdn are set. This is still the default so in most cases it's
no difference, but at least we have centralized all use of facter to one...

Fixes #19833 - Fix Rails/FindEach cop

Fixes #20146 - domain-less server email errors fixed

Fixes #17588 - Remove 1.16 deprecations

show_taxonomy_tabs helper, Settings.method helper and email.yaml support

Fixes #17330 - skip admin email if it's unknown

When admin user is being seeded the Setting might not exist at that
moment. We can't just create it with value, since the setting would
be invalid because of other attributes. Therefore we split settings
creation from the setting list so we could create it from seed too....

Fixes #12156 - Adds email configuration into Foreman settings

Instead using email.yaml, the email configuration
can be modified dynamically via settings.