chore: implement leastlatency LB with Peak EWMA

[igorbernstein2]

Other changes

• Hook up subset size settings
• Increase PeakEwma decay - AFE latency is very noisy so we need a long duration to discern which AFEs genuinely perform better

Change-Id: I138501487d4dec53aa80e18785023bcbfaa06807

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Fixes #<issue_number_goes_here> ☕️

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