Fix #727 - HSTS: default preload to off

[swalkinshaw]

The HSTS preload option defaulted to true. This turns it off by default since the HSTS preload list should be opt-in as it also requires a submission to https://hstspreload.org.

NOTE: If you submitted your site to the HSTS preload list and want to keep using the preload option, then set the variable:

# group_vars/production/wordpress_sites.yml (example)

example.com:
  # rest of site config
  ssl:
    enabled: true
    provider: letsencrypt
    hsts_max_age: 31536000
    hsts_include_subdomains: true
    hsts_preload: true

Or set the global default:

nginx_hsts_preload: true

See https://roots.io/trellis/docs/ssl/ for more information.

[swalkinshaw]

Doc updates with much more information on this: roots/docs#66