Saved configuration in chart

Follow up https://gitlab.com/gitlab-org/gitlab-ee/issues/7478 to have a saved configuration, so when you return to it (or anybody), it will have the same saved configuration.

A saved configuration is the same as a saved configuration for an issue board. It is a scoping associated with the board itself.

This is different from saved filters, which are per user: https://gitlab.com/gitlab-org/gitlab-ee/issues/10437