[CBBS] Backup Service should allow read-only admins to view the Backup Service

Currently, read-only admins cannot see any part of the Backup Service in the UI or run any of the Backup Service APIs.

This is not acceptable to many customers, as read-only administrative users often monitor clusters and check that backups have completed.

For example, a backupfulladmin can see the task history for a Backup Service backup using the below API command:

curl -X GET http://localhost:8097/api/v1/cluster/self/repository/active/bucket1_backup/taskHistory -u backupfulladmin:password

But, the readonlyadmin gets this error when using the same API command:

{

  "message": "Forbidden. User needs one of the following permissions",

  "permissions": [

    "backup_admin"

  ]

}

The below APIs are commonly used for monitoring the Backup Service backups – these and other Backup Service GET APIs should be allowed for read only admins.

/api/v1/cluster/self/repository/active

/api/v1/plan/<plan-name>

/api/v1/cluster/self/repository/active/<job-name>/taskHistory