Adds govuk_app_config to list of applications
Adds govuk_app_config to list of applications

This will import useful things such as the health check document: https://github.com/alphagov/govuk_app_config/blob/master/docs/healthchecks.md

Have also added the missing `sentry_url`/`dashboard_url` overrides for govuk-docker.
alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs