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.
In preparation for embedding specific metrics in issues
https://gitlab.com/gitlab-org/gitlab-ce/issues/62971,
this commit moves the BaseService for metrics dashboards
to a new services subdirectory. This is purely for the sake
of organization and maintainability.
