Add /healthcheck endpoint
Add /healthcheck endpoint

Once enabled in puppet, this will make sure we have a more valuable
healthcheck than currently.

https://github.com/alphagov/govuk-puppet/blob/master/modules/govuk/manif
ests/apps/signon.pp#L90

alphagov/signonotron2,alphagov/signonotron2,alphagov/signonotron2,alphagov/signonotron2