📖 Small improvements to in-place update proposal

[fabriziopandini]

What this PR does / why we need it:
This PR makes a few small improvements to the in-place update proposal dropping some confusing wording/examples, probably left over from previous iterations. Most specifically:

• It drops wording that might lead readers to think that we are giving users the chance to influence the in-place decision (the decision is always deferred to the runtime extension)
• it drops examples where we are changing the API (it was decided to not perform API changes in this first iteration)

/area documentation

[stmcginnis]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: edf4fe32efad500fc3333477d8af60a157dce565

[furkatgofurov7]

/lgtm

[sbueringer]

Thx!

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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