Protect conditionUpdate against concurrent access

[joelrebel]

Condition Updates through the API require the ResourceVersion field to be updated in sequence to ensure concurrent updates are not overwriting each other.
In #15 we add support for Condition Updates to be received through events, and since these events are a stream - with no request, reply mechanism the controller has no way to query the current ResourceVersion before sending out the update.

We need a better strategy to ensure updates are applied in order of them being published.

Originally posted by @DoctorVin in #15 (comment)