Add Purchase Credits card to SM admin page

What does this MR do and why?

Add Purchase Credits card to SM admin page

Retrieve credits from CDot Create new card component

Changelog: added EE: true

References

Screenshots or screen recordings

Before	After
	Tier: Free Trial - 24 included credits (Removed) Trial - included credits with purchased monthly credit (Removed) Error state

How to set up and validate locally

1. Set up GDK in Self managed: GITLAB_SIMULATE_SAAS: 0

2. Sign in, go to http://localhost:3000/admin/subscription

   • Go to http://127.0.0.1:3000/rails/features/
     • Turn on FF sm_purchase_credits

3. Validate various states:

   1. Free, no credits - remove all licenses

4. Trial - click on "Start free trial" , fill out the form

   1. Navigate back to http://localhost:3000/admin/subscription after signup
   2. If you still have hte patch applied, you should still only see the trial credit amount (24)

5. Paid subscription

   1. Sign in to https://customers.staging.gitlab.com/
   2. Purchase a SM Ultimate subscription, note activation code
   3. Navigate back to http://localhost:3000/admin/subscription
      1. Click "Add Activation code" and apply code
   4. You should not see the GitLab Credits card anymore

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #595574