Provide for Drupal 8's trusted_hosts setting

[tizzo]

In Drupal 8 there's a new setting called trusted_hosts. This is interfering with probo builds. We should consider having the Drupal plugin append a snippet in settings.php for Drupal 8 sites like:

$settings['trusted_host_patterns'] = array(
  '^localhost$',
  '^.+\.probo\.build$',
);

[heddn]

If you do what platform.sh does, you can reference & include a settings.probo.php based on the existence of an environment variable. Then insert the hostname dynamically as well.

[sk33lz]

See https://github.com/platformsh/platformsh-example-drupal8/blob/master/scripts/platformsh/dist.settings.php#L35.

[greggles]

For anyone else who finds this, a potential solution today is using the settingsAppend feature of the Drupal plugin:

    settingsAppend: |
      $settings['trusted_host_patterns'] = array(
        '^localhost$',
        '^.+\.probo\.build$',
      );