Allow users to configure default panels

There are a bunch of default panels for request rates and latencies, and Sidekiq worker rates.

However, some groups are now adding their own graphs, that provide better clarity into how the features are performing. This means that the default graphs become less important. It is already possible for the groups to add their graphs higher up on the dashboard, or remove them completely by excluding the component.

In gitlab-com/runbooks!3416 (comment 544521207) it was brought up that it would be handy to be able to collapse some of the default rows on the stage group dashboard from their configuration.