NLB-5919 Inform users of the new nginxaas.capacity.percentage metric

[arussellf5]

Proposed changes

Problem: The NGINXaaS project is phasing out the old consumed NCUs metric and replacing it with the new, more accurate, percentage capacity metric.

Solution: We are informing users of the change, urging them to make use of the new percentage capacity metric and modifying our guidance about scaling to reflect the change.

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[github-actions]

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[arussellf5]

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