DRY definition of AI Gateway and Cloud connector headers
Related to !153440 (comment 1920871670)
There are multiple places across libs and REST API where we define same set of AI GW headers sent with AI GW requests. Ideally these should be defined on single place (parhaps as part of AI GW client) and re-used where needed.
Related to this, there is also cloud_connector_headers
API helper method, but it's re-used/included not only on API layer, but also in AI GW client libs - ideally these helper method should be be moved to a Cloud COnnector library so we avoid re-using REST API helper from a lower-level library.