Create Group Usage Quotas view in Core

What does this MR do and why?

This MR creates an endpoint and a view for the Usage Quotas page in the Core codebase, so that Usage Quotas is available for Community Edition (&7176 (closed))

Implements: #371820 (closed)

MR Cadence

Description	MR
Move :read_usage_quotas policy to Core app	!103021 (merged)
Create Usage Quotas route/controller/view in Core	👈 you're here
Add menu entry on sidebar	!106083 (merged)

Screenshots or screen recordings

EE and SaaS

FF off	FF on

EE unlicensed

• Removing your license in: http://gdk.test:3000/admin/subscription

FF off	FF on

CE

export FOSS_ONLY=1 && gdk restart

FF off	FF on

How to set up and validate locally

We need to validate this in 4 scenarios:

1. GitLab EE: by having a test license in your GDK.
2. GitLab SaaS: setup a license like the above and simulate SaaS
3. GitLab EE Unlicensed: by removing your license in http://gdk.test:3000/admin/subscription
4. GitLab CE: by executing
   1. export FOSS_ONLY=1
   2. gdk restart

Now go to any Group Usage Quotas: http://gdk.test:3000/groups/flightjs/-/usage_quotas and check if your local setup matches the screenshots.

• To enable the FF: Feature.enable(:usage_quotas_for_all_editions)
• To disable the FF: Feature.enable(:usage_quotas_for_all_editions)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.