Add a sentry_dsn parameter for CKAN
Add a sentry_dsn parameter for CKAN

We want to start reporting errors to Sentry so we'll need this
configuration option available.

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