Add UserOverridesList component with data fetching and pagination

What does this MR do and why?

Adds a draft per-user budget cap overrides list on the Credit Caps page. This MR focuses on API integration, error handling and pagination.

MR series

#	MR	Status
1	Add UserOverridesList component with data fetching and pagination	✅ This MR
2	Add read-only table with editable inputs and toggles	TBC ⏳
3	Add Save and Remove buttons with mutation	TBC ⏳
4	Add no-op "Add override" button	TBC ⏳

References

• Related to https://gitlab.com/gitlab-org/gitlab/-/work_items/624327

Screenshots or screen recordings

before	after

How to set up and validate locally

Prerequisites: self-managed GitLab instance with the Credits Dashboard enabled. .

1. Enable SM

2. Open /-/graphql-explorer

3. Find some user's Global IDs

query {
  users { # OR users(usernames: ["alice.smith"])
    nodes {
      id
      name
      username
    }
  }
}

2. Create a per-user cap override for the found users (can use gid://gitlab/User/1 for admin)

mutation ($overrides: UpsertUserBudgetCapOverridesInput!) {
  upsertUserBudgetCapOverrides(input: $overrides) {
    userOverrides {
      cap
      capEnabled
      user {
        username
      }
    }
    errors
  }
}

with variables:

{
  "overrides": {
    "overrides": [
      {
        "userId": "gid://gitlab/User/1",
        "cap": 20,
        "enabled": true
      }
    ]
  }
}

3. Open http://localhost:3000/admin/gitlab_credits_dashboard/credit_caps
4. Verify that new records show-up in the JSON output

Alternatively

1. Start Storybook yarn storybook:start
2. Verify these stories work:
   • http://localhost:6006/?path=/story/ee-usage-quotas-wallet-agnostic-credits-dashboard-credit-caps-app--overrides-empty
   • http://localhost:6006/?path=/story/ee-usage-quotas-wallet-agnostic-credits-dashboard-credit-caps-app--overrides-paginated

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.