[Reseller] Show modal to let users know they can't buy storage or minutes on GitLab for reseller subscriptions

Problem

As per this discussion, if the subscription was sold via reseller, we should not allow customers to purchase storage or CI minutes.

customers-gitlab-com#4946 (closed) takes care of this on CustomersDot portal. We also need to do the same on GitLab by showing a message which informs the user why they can't purchase when they click on any of the below buttons.

#378596 (closed) will handle the add seats buttons.

Flow	Screenshot
Buy additional minutes (Usage quotas page)
Buy storage (Usage quotas page)
Purchase more storage (Usage quotas page)

Proposal

When any of the above buttons are clicked, show a modal letting the user know that their subscription is in read-only mode and can't be modified.

Description	MR	Status
Update CDot to expose eligible_to_buy_ci_minutes and eligible_to_add_storage? as fields in subscription_type.rb	https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/7292	workflowcomplete
Send limited_access_reason to GL	https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/7329	workflowcomplete
Introduce FF and the modal	!129790 (merged)	workflowcomplete
Wire up the modal and API call	!130457 (merged)	workflowcomplete
Use limited_access_reason to show a different text on the modal	!131533 (merged)	workflowcomplete
Trigger modal from buy minutes	!132509 (merged)	workflowcomplete
Trigger modal from buy storage	!131695 (merged)	workflowcomplete

Mockup: #378596[Message_when_reseller_customer_tries_purchasing.png]