docs: Add example for non map Arrays

[david-martin]

What this PR does / why we need it:

Adds an example for mapping metrics from a non-map Array.

See https://kubernetes.slack.com/archives/CJJ529RUY/p1692264377694619 for where this request came from.

How does this change affect the cardinality of KSM: (increases, decreases or does not change cardinality)

Does not change cardinality as it relates to CustomResourceStateMetrics

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 n/a

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[mrueg]

/triage accepted

/assign rexagod

(as he commented on slack)

[rexagod]

/lgtm
Thank you, @david-martin! 🎉

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: david-martin, rexagod

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