[Docs][Permission] GCP medium permission set cannot pass sky check

[cblmemo]

The medium permission detailed in our doc seems outdated. Current:

roles/browser
roles/compute.admin
roles/iam.serviceAccountAdmin
roles/iam.serviceAccountUser
roles/serviceusage.serviceUsageConsumer
roles/storage.admin
roles/iam.securityAdmin

However, when I tried this on a service account, I got:

$ sky check gcp
Checking credentials to enable clouds for SkyPilot.
  GCP: disabled                              
    Reason: The following permissions are not enabled for the current GCP identity (<service-account-email-address> [project_id=<project-id>]):
    {'serviceusage.services.enable'}
    For more details, visit: https://skypilot.readthedocs.io/en/latest/cloud-setup/cloud-permissions/gcp.html
No cloud is enabled. SkyPilot will not be able to run any task. Run `sky check` for more info.

When I manually change the roles/serviceusage.serviceUsageConsumer to Service Usage Admin, it works for me:

$ sky check gcp
Checking credentials to enable clouds for SkyPilot.
  GCP: enabled                              

To enable a cloud, follow the hints above and rerun: sky check 
If any problems remain, refer to detailed docs at: https://skypilot.readthedocs.io/en/latest/getting-started/installation.html

🎉 Enabled clouds 🎉
  ✔ GCP