As part of the an effort to ensure compatibility from different data
sources, the dashboard "normalized" data to ensure data will always
available.

Now that the compativblity is not needed thanks to
https://gitlab.com/gitlab-org/gitlab/merge_requests/15709,
the data sources are uniform again.

Objects in dashboard store have been renamed from

- dashboard[].metrics to dashboard[].panels
- panel[].queries to panel[].metrics

Other components that depend in this data have been updated, added
empty data checks so components work while the dahboard loads. Embed
component also considered.