feat: minor updates to arrays

[toumorokoshi]

• lowered guidance to should (since it is not critical for an auto-generated client)

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[toumorokoshi]

I started taking a stab at this, but before I get deeper - I'm having mixed feels about the existing guidance around allowing single-element add/delete custom methods: https://aep.dev/144#update-strategies.

I feel like we could do better - probably just relying on json patch: https://jsonpatch.com/

[mkistler]

Looks good. 👍

Left one little suggestion.