[Reseller] Add message letting user know that they can't renew, purchase storage, CI minutes, seats on GitLab
## Problem
As per this [discussion](https://gitlab.com/groups/gitlab-org/-/epics/8941#note_1135229635), if the subscription was sold via reseller, we should not allow customers to purchase seats, storage or CI minutes.
https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/4946 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.
| Flow | Screenshot |
| ------ | ------ |
| Add seats (Usage quotas page)|  |
| Buy additional minutes (Usage quotas page)| |
| Buy storage (Usage quotas page)| |
| Purchase more storage (Usage quotas page)|  |
| :x: ~~Add seats (Billing page)~~ we hide this button for resellers |  |
## 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.
Mockup: https://gitlab.com/gitlab-org/gitlab/-/issues/378596/designs/Message_when_reseller_customer_tries_purchasing.png
epic