Issue Summary

Currently, retrieving space admin information for all spaces in Confluence Cloud requires either:

• Site Admin access (to use the Admin Key header Atl-Confluence-With-Admin-Key: true), or
• Explicit space membership on every space

This creates a significant gap for Enterprise customers who need to automate space governance tasks, such as identifying space admins for access requests, checking for space key collisions during migrations, or notifying space owners of org-wide activities — without granting full Site Admin rights to an automation account or service account.
Product Admins can view all spaces and their admins in the Confluence Admin UI, but there is no equivalent API capability scoped to Product Admin permissions.

Requested Behaviour
Expose one or both of the following:

•  A Product Admin-scoped API endpoint (or an equivalent scope/header) that allows a Product Admin account or service account with Product Admin rights to:
             List all spaces (regardless of space-level membership)
             Retrieve space permission grants (including space admins) for any space
   
• Extend the Admin Key mechanism to support Product Admin users (not just Site/Org Admins), so automation accounts can be granted the minimum necessary privilege to perform space enumeration without being full Site Admins.