Change Management: no elective changes unless metrics are working

Why is this change being made?

Adding a policy that infrastructure changes cannot go ahead unless the metrics platform is functioning correctly.

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what

cc @brentnewton @marin @dawsmith @AnthonySandoval @glopezfernandez @sloyd