[SaaS] Alert to group Owners when group is approaching seat count

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.

Intended users

• Group Owners
• Only groups enrolled in quarterly subscription reconciliation. See exactly which use cases we're solving for in the Epic description.

Proposal

Group Owners should notified when the group is approaching its seat count.

Design here

What triggers the alert?

When a user is added that increases the number of Max seats used:

• If Max seats used < Seats in subscription, trigger the alert based on the percentage of Seats currently in use / Seats in subscription per the table below
• If Max seats used >= Seats in subscription, the alert should not be triggered.

Seats in subscription	Notified at
0-15	No percentage, notify at 1 seat left
16-25	No percentage, notify at 2 seats left
26-99	10 %
100-999	8%
1000+	5%

Who should see the alert and where?

• Only visible to group Owners of the top-level group
• Alert is shown on all pages of the group/subgroup/project within the parent group (See conversation about where to show this alert)
• Alert is dismissible – it will stay dismissed (at least until it's triggered again by another seat being added)

Note that this is a very similar alert to the one in SM implemented here, but with slightly different logic.

Implementation plan

Description	MR
Introduce Seat Count Alert and Helper backend / frontend	!77865 (merged)
Update CDot to send reconciliation status backend	now an issue: customers-gitlab-com#3934 (closed)
Introduce call to CDot to fetch reconciliation status backend	shared client part of issue: customers-gitlab-com#3934 (closed)
Introduce Callout functionality with custom display logic backend / frontend	!78260 (merged)
Plug in all logic to display Seat Count Alert backend	!79563 (merged)