Add frontend code to support storage_enforcement_banner

What does this MR do and why?

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/349690

This adds the frontend code to support Pre-enforcement storage notifications

Separation	MR link
backend	!79624 (merged)
frontend	👈 you're here

This also adds initVueAlerts to main.js. I believe it's a cheap piece of code and would avoid the hassle of including it in all groups and projects pages manually

Screenshots or screen recordings

How to set up and validate locally

1. Add a date in the future for storage_enforcement_date in app/models/namespace.rb
2. Go to a free group's page, or free group's project's page
3. Make sure the banner in the screenshot is showing

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.