Add 'deprecated' and 'not_used' to metrics definitions status list

Proposal to add more options to metrics definition status list.

• deprecated indicates that the metric is deprecated and should not be used, planned to be removed, possibly having an issue to remove the metric

• not_used indicates that the metric is not used in any dashboard

Proposal

• Add deprecated not_used in JSON metrics schema
• Document new statuses https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/development/usage_ping/metrics_dictionary.md

cc @gitlab-org/growth/product-intelligence/engineers