Wire up API to show modal for reseller subscriptions

What does this MR do and why?

Call CustomersDot GraphQL API to determine if we should show a modal when subscription is not allowed to add seats

Screenshots or screen recordings

No modal flow	Modal flow
Screen_Recording_2023-09-04_at_16.08.15	Screen_Recording_2023-09-04_at_15.49.36

How to set up and validate locally

• Create a ramp subscription
• Create a reseller subscription
• Create a subscription without either reseller or ramp attributes
• Run rails c and then `Feature.enable(:limited_access_modal)

For both ramp + reseller subscriptions:

• Link it to a GL namespace either in the CDot UI (subscriptions/SUBSCRIPTION_NAME/edit?transaction=change_gitlab_group) or via the rails console
• In GL, navigate to /groups/GROUP_NAME/-/usage_quotas#seats-quota-tab
• Verify that Add seats button appears as usual
• Verify that clicking the button displays the modal
  • By default, it will show the modal text for a reseller subscription because we're temporarily stubbing the limitedAccessReason
  • To see the ramp subscription text, you can modify this line to return RAMP_SUBSCRIPTION
• Verify that closing out of the modal functions properly

For the regular subscription:

• Link it to a GL namespace either in the CDot UI (subscriptions/SUBSCRIPTION_NAME/edit?transaction=change_gitlab_group) or via the rails console
• In GL, navigate to /groups/GROUP_NAME/-/usage_quotas#seats-quota-tab
• Verify that Add seats button appears as usual
• Verify that clicking the button takes you to CDot to add seats

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 #409750 (closed)