[Fleet] Improve UI for agent upgrade in batches to hide complexity

[juliaElastic]

As a side effect of bulk actioning in batches in 8.4, the UI shows now multiple banners when agent upgrade is executed in batches.

This is because for each batch execution, there is a new entry created in .fleet-actions index, and the UI shows a banner for each (returned by /current_upgrades API).

This can be confusing to users, they should not be exposed to the complexities of how bulk action is executed.

To improve, Fleet could store a new field (e.g. originatingId) in .fleet-actions that would associate the action documents originating from the same action.
The UI then could read this field, and show only one banner for multiple actions having the same originating id.
In case of abort, the UI would send abort on all action ids that belong to the same originating id.

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[juliaElastic]

this improvement would become unnecessary if we moved action batching to Fleet Server #141567

[nchaulet]

@juliaElastic it's already possible to get multiple action with the same action_id, I think we just missed to use the same action for every batch, and the endpoint that is used to show the current upgrade is already supporting this, (I created a PR to demo this here #136663)