Grafana private to public dashboards sync is broken

Failing due to the partial implementation of the migration. We have new hosts for grafana and prometheus, but we didn't add them to the chef vaults.

The scope of this issue is to make it work again as is.

Further corrective actions are:

• Extract grafana dashboards sync out of the default grafana recipe https://gitlab.com/gitlab-com/infrastructure/issues/2017
• Hold grafana version in the gitlab-grafana cookbook https://gitlab.com/gitlab-com/infrastructure/issues/2016