🐛 ClusterClass variable schema: drop multipleOf, change min/max to *int64

[sbueringer]

Signed-off-by: Stefan Büringer buringerst@vmware.com

What this PR does / why we need it:
This PR changes min/max fields to *int64 and drops multipleOf entirely (as it's not that useful).

I though I had tested json.Number entirely, but I forgot a use case. When using the structs on client-side and sending a json.Number to the server it is marshaled as follows:

• 1.5, "1.5" => 1.5
• 1, "1" => 1
  This does not match the OpenAPI schema validation of string or even "int or string". So we cannot use json.Number as the marshaling behavior is not what we want.

Using float64 is not recommended:

found float, the usage of which is highly discouraged, as support for them varies across languages. Please consider serializing your float as string instead. If you are really sure you want to use them, re-run with crd:allowDangerousTypes=true
Error: not all generators ran successfully

So we could use IntOrString (floats would have to be serialized as strings), but let's start with int64 for now as that covers the most use cases. If we want to support floats later on we can tackle that later, although it's not 100% a compatible change to change the field from int64 to intorstring ("Going from int->intorstring is a ~compatible change from API schema perspective, not from code").

xref: lenghty Slack thread discussing the options / prototyping: https://kubernetes.slack.com/archives/C8TSNPY4T/p1635175756089200

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

[vincepri]

/lgtm

[k8s-ci-robot]

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Test name	Commit	Details	Required	Rerun command
pull-cluster-api-apidiff-main	86f58e4	link	false	/test pull-cluster-api-apidiff-main

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[sbueringer]

/cc @fabriziopandini @randomvariable

[fabriziopandini]

/lgtm

[vincepri]

/approve

[k8s-ci-robot]

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