feat DO-1856: add option for CPU scaling

[TheOrangePuff]

Description of the proposed changes

• Allow easily overriding the targetUtilizationPercent value
• Change the default to much lower to actually scale with load. Prerender CPU load is quite bursty so an average CPU of 10% means it's under quite a bit of load. The max average I've seen is only 25% so the previously set 50% would never trigger.

Notes to reviewers

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