Add projects with invited groups to the free user cap overage email

What does this MR do and why?

Add projects with invited groups to the free user cap overage email

• iterative next step to finish the feature that is behind a feature flag.
• allows correct notification when a project inside a free namespace has invited a group that then adds users that cause the free namespace to go over the limit.
• see #415487 for more details and the 'why'

Screenshots or screen recordings

no change from recent implementation

Click to expand

html	text

How to set up and validate locally

1. Setup initial application settings in bundle exec rails c

   ApplicationSetting.first.update(dashboard_limit_enabled: true, dashboard_limit: 5)
   Feature.enable(:free_user_cap_over_limit_email)

2. Simulate Saas and restart GDK
3. Create a new top-level private group(A).
4. Create a new project under group A project(P).
5. Create a public(for ease of example so limit isn't applied) new top-level group(B).
6. Go to the project A's member page and invite group B.
7. Confirm on page reload no free user cap alerts exist(yet) and members are under 5.
8. Go to the members page of group B and invite 6 users by username.
9. Go to the members page of group A and confirm over limit alert message appears(not added by this MR).
10. Go to http://gdk.test:3000/rails/letter_opener/ and verify email is seen.

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.

Related to #415487