Mark specialist-publisher-rebuild as internal only
Mark specialist-publisher-rebuild as internal only

This app will be available to the public, but initially,
it's requests will be proxied through from version 1.

Fixes: https://github.com/alphagov/govuk-puppet/issues/4389

specialist-publisher-rebuild-standalone is left as is, because that is a
separate integration-only instance for development uses only and will be
accessed directly.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet