Return license with activation mutation

What does this MR do?

Part of https://gitlab.com/gitlab-org/gitlab/-/issues/325541

Depends on !57382 (merged) base branch needs to be changed to master after dependency was merged.

The existing GraphQL mutation to activate a license needed some modification to meet requirements for the new license page.

When activating a license via the GraphQL mutation, the mutation previously returned clientMutationId and errors. For the new license page it will now return the activated license as license and the kept errors. The clientMutationId is not needed anymore and was removed. With these returns we will be able to render the changes of the (newly) activated license without having to reload the page or to query another endpoint.

Note: The new return value license for the mutation will be used in another merge request in the frontend. When I added it here it raised a linting error so I left a note in the issue about that.

Mutation

mutation($gitlabSubscriptionActivateInput: GitlabSubscriptionActivateInput!) {
  gitlabSubscriptionActivate(input: $gitlabSubscriptionActivateInput) {
    license {
      id
      type
      plan
      name
      email
      company
      startsAt
      expiresAt
      activatedAt
      lastSync
      usersInLicenseCount
      billableUsersCount
      maximumUserCount
      usersOverLicenseCount
    }
    errors
  }
}

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