design-proposal: instancetype.kubevirt.io - Support custom resource sizing

[lyarwood]

What this PR does / why we need it:

Instance types and preferences provide a way to define common VirtualMachine workload resource sizing and preferences.

The common-instancetypes project within KubeVirt currently provides a set of standardized instance types and preferences that can be deployed by virt-operator alongside all of the other core KubeVirt components.

While the resources provided by the common-instancetypes project are a great starting point they are generalized and could never possibly cover all workload resourcing and preference use cases.

As such this design proposal seeks to make it as easy as possible for both cluster admins and users to create their own customized versions of these commonly deployed resources specific to their workloads. Additionally the instance type API itself will be made more flexible by making vCPU and memory resource sizing optional within an instance type, allowing users to provide their own sizing within their VirtualMachine while still retaining the remaining benefits of using an instance type.

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 #

Special notes for your reviewer:

Checklist

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Release note:

NONE

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[jean-edouard]

Lots of pedantic formatting comments, feel free to ignore.
My only real question is around the need for a new virtctl command.
Thanks!

[jean-edouard]

Why? Can't users just kubectl edit to make changes?

[lyarwood]

The use case with virtctl customize is that we want to start with an object in the cluster, make some small changes, automate kind conversion/metadata removal and then output the newly crafted definition.

Does kubectl edit actually support taking an existing object and only outputting the result locally? I thought it always attempted to mutate the object in the cluster?

[lyarwood]

Lots of pedantic formatting comments, feel free to ignore. My only real question is around the need for a new virtctl command. Thanks!

Thanks @jean-edouard , really appreciate the review!