Explictly state that MTTP is tracking changes in gitlab-org/gitlab project and gitlab.com

Why is this change being made?

MTTP is measuring specifically time for gitlab-org/gitlab project and gitlab.com environment.

Previous wording was not clear on what projects are involved (For MTTP only gitlab-org/gitlab is tracked), and what the production environment is (For MTTP only gitlab.com and not canary) is tracked.

Does this MR meet the acceptance criteria?

Conformity

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