Add the kubernetes.io/os selector too

[aleskandro]

In the future, it might be good for us to include the OS matchExpression too.
it is a good piece of information that is also worth considering for the scheduler predicates.

For example, windows container images shouldn't "risk" landing into a linux node.

The current official recommendation (for OCP) is to leverage runtime classes that instruct the scheduler as a kind of 'side-effect'/additional feature, so it's just a "possible" future thing that we can onboard for free to consider better the platform information in the manifest list images we inspect

xref #44 (comment)

[Prashanth684]

As we do more additions like this, we should start thinking when we want to expose our features with opt-in flags or options in the CR rather than doing it implicitly under the covers, like something along the lines of:

affinitySelector:
     - architecture
     - osType
     - custom

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