https://gitlab.com/gitlab-org/gitlab-ce/issues/62971
Adds support to EnvironmentsController#metrics_dashboard
for the following params: group, title, y_label
These params are used to uniquely identify a panel on
the metrics dashboard.
Metrics are stored in several places, so this adds
utilities to find a specific panel from the database
or filesystem depending on the metric specified.
Also moves some shared utilities into separate classes,
notably default values and errors.
This refactors common metrics importer for two reasons. 1. To create a
new pattern that can be followed by future importers that will minimize
dependency collision and 2. To allow EE to more easily extend
dependencies.
