Include license changes in pricing and tier DRI responsibilities

The e-group came away with some concerns (see https://gitlab.slack.com/archives/C5W3VS1C4/p1571679529081900 for the response to the conversation) regarding the impact of gitlab-org/gitlab#22257 (closed) on GitLab's revenue.

To reduce the likelihood of possible risk being introduce into a release in the future, this MR extends the CEO's DRI rule to product changes that directly impact seat calculations as well as pricing/tiers.