Consider aligning Cluster API conditions to upstream conditions

[sbueringer]

A while back an upstream KEP was merged which tries to standardize conditions: https://github.com/kubernetes/enhancements/tree/master/keps/sig-api-machinery/1623-standardize-conditions
(corresponding implementation: kubernetes/kubernetes#90454)

The diff to our conditions is:

• upstream has an additional optional ObservedGeneration field
• Cluster API has an additional optional Severity field

I think it could be interesting to consider if we want to add the optional ObservedGeneration field to our Conditions.

godoc:

	// If set, this represents the .metadata.generation that the condition was set based upon.
	// For instance, if .metadata.generation is currently 12, but the .status.condition[x].observedGeneration is 9, the condition is out of date
	// with respect to the current state of the instance.
	// +optional
	ObservedGeneration int64 `json:"observedGeneration,omitempty" protobuf:"varint,3,opt,name=observedGeneration"`

Recently there was a thread about this in #sig-api-machinery https://kubernetes.slack.com/archives/C0EG7JC6T/p1666371350588619

/area api

[One or more /area label. See https://github.com/kubernetes-sigs/cluster-api/labels?q=area for the list of labels]

[sbueringer]

cc @fabriziopandini @dlipovetsky

[fabriziopandini]

/triage accepted
I have written https://docs.google.com/document/d/1hBQnWWa5d16FOslNhDwYVOhcMjLIul4tMeUgh4maI3w/edit some time ago with similar considerations, which is also linked by our meeting minutes in the open proposal section

[fabriziopandini]

/kind api-change

[k8s-triage-robot]

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/remove-triage accepted

[fabriziopandini]

/priority important-longterm

[fabriziopandini]

/triage accepted
/assign

It definetly makes sense.
I will take a look about starting getting rid of our limitation about only positive polarity + make a first assesment about other differences.
cc @theobarberbany