Fix frontend for local docker dev environment
Fix frontend for local docker dev environment

Custom alias domains such as http://frontend.dev.gov.uk are not working
on any apps running Rails 6, due to the addition of "Host Authorisation"
middleware so we need to explicitly add the local domain to their
`config.hosts`.

Similar commit: https://github.com/alphagov/maslow/pull/546/commits/864e3ddf57f3cf2b6007873c817d11629ba61485

Issue on govuk-docker: https://github.com/alphagov/govuk-docker/issues/176

Trello card: https://trello.com/c/Ik7ulDXQ/1768-3-upgrade-info-frontend-to-rails-6

alphagov/frontend,alphagov/frontend,alphagov/frontend,alphagov/frontend