[SaaS] Add messaging about user overage process to Renewal flow
## Problem to solve
SaaS customers are being surprised and taken off-guard by Quarterly Subscription reconciliations. Because self-service SaaS customers have not historically been charged true-ups, the QSR process and the fact that they have to pay for overages is totally new. See tickets from customers [here](https://gitlab.com/gitlab-org/fulfillment-meta/-/issues/337).
## Intended users
**This issue is just for SaaS customers.**
* Group Owners who are **renewing a subscription** through our self-service renewal flow
* See exactly which use cases we're solving for in the [Epic description](https://gitlab.com/groups/gitlab-org/-/epics/7229#saas-customers).
## Proposal
When a user is **renewing** GitLab, make sure that they are aware of the overage process. Show a message to all customers using the self-service renewal flow that notifies them about the overage process.
[Purchase Design here](https://gitlab.com/gitlab-org/gitlab/-/issues/347267/designs/Option_2__Alert_during_checkout_informing_user_of_QSR.png), could we reuse for renewal flow?
Link for `How does billing work?`: `https://docs.gitlab.com/ee/subscriptions/quarterly_reconciliation.html` (shared [here](https://gitlab.com/gitlab-org/gitlab/-/issues/347267/designs/Option_2__Alert_during_checkout_informing_user_of_QSR.png#note_828638740))
issue