Show contact information notice when billing account is present

What does this MR do and why?

Related to #432421 (closed)

When user has the key_contacts_management flag enabled, show the Contact information notice instead of billing address.

This will be altered to check for billing account presence with [Key Contacts Management] Fetch billing account... (#432420 - closed).

Screenshots or screen recordings

New subscription

Before	After

Add-on plan

Before	After

How to set up and validate locally

1. Ensure you have CustomersDot running with a customer with a billing account

   • A billing account is created when the first subscription is purchased

2. In the GitLab rails console, enable the key_contacts_management feature flag

   Feature.enable(:key_contacts_management)

3. Navigate to http://localhost:3000/-/subscriptions/new?plan_id=2c92c0f876e0f4cc0176e176a08f1b70

4. Verify that you are able to navigate to the Contact information step

5. Verify that the billing address data does not show

6. Verify that you can go back to Edit the first step

7. Verify that you can navigate to the purchase step

8. Disable the FF

   Feature.disable(:key_contacts_management)

9. Verify that the page still shows the Billing address step

10. Verify that the step shows the correct data

11. Verify the same at http://localhost:3000/-/subscriptions/new?plan_id=2c92c0f9699eca030169a2f1f117045f, which hits the addon component logic

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.