Make action optional when upgrade details are provided

[michalpristas]

In a context of agent migration.

When agent is migrated and still has some upgrade details or upgrade was triggered manually for some reason we should reflect that in UI.

This PR makes action optional and updates upgrade details anyways.

I'd like ACK handling of upgrade to be reworked, but ideally in a separate PR to lower risk as I'd like this one to be in 9.2

Fixes: #5564

[prodsecmachine]

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[blakerouse]

Sorry I am having trouble following how this PR works.

Does this fix the issue where if you check-in to a new cluster for the first time after migrate that it will reflect the upgrade state of that agent? If so, could you walk me through how this is done in this code.

[cmacknz]

@michalpristas is this PR still relevant?

[michalpristas]

Yes it is

[michel-laterman]

The PR is doing a few things; the changes to allow for missing actions (in case of migrations) makes sense; however I don't understand why the ack endpoint is being changed, or why the status is not being set to nil if a checkin indicates an upgrade completes.

Also can you please add a changelog fragment

[michalpristas]

code cleanup: moved updgrade status removal to a separate PR: #5970
now this change should be cleaner and more readable

[michel-laterman]

lgtm