Update Self-Managed docs

- Add Cloud Licensing details
- New page for Quarterly subscription reconciliation

doc/subscriptions/quarterly_reconciliation.md

+---
+stage: Fulfillment
+group: Purchase
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
+---
+
+# The quarterly subscription reconciliation process
+
+GitLab reviews your seat usage every quarter and sends you an invoice for
+any overages.
+
+Annual reviews, also known as the [annual true-up process](self_managed/index.md#users-over-license),
+require you to pay the full annual subscription fee for users added anytime during the year. With quarterly
+reviews, you only pay for the remaining period of your subscription term.
+
+For example, if you add users in the third quarter of your subscription term, you only
+pay 25% of what you would have paid previously. This results in substantial savings.
+
+If it's not possible for you to participate in quarterly reconciliations, you can opt out of the
+process by using a contract amendment. In that case, you default to the annual review.