update mktg global scoped labels

Why is this change being made?

The Marketing global scoped labels were elevated from the Marketing Group to the GitLab.com level and they were slightly modified to identify they belonged to Marketing. This is to allow our web design team the ability to leverage the same labels as the rest of the marketing organization without duplicating the labels.

/mention #6141 (comment 266999271) /mention https://gitlab.com/gitlab-com/marketing/marketing-operations/issues/1750

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