Dashboard import and export for DevOps Monitoring

As part of the readiness review and an evaluation of features we should be dogfooding we are looking at feature gaps between what we currently have on dashboards.gitlab.net and what is possible using built-in application metrics.

This feature request is to add the capability to export and import dashboards so it is possible to put dashboard configurations under source control. This is an essential feature of Grafana and is used by GitLab.com for monitoring. We are slowly moving all of our service dashboards to jsonnet which allows for a bit more reuse and flexibility in creating a rich set of dashboards. To start, it would be helpful if the monitoring feature had a similar export/import functionality.