Resolve "Add the pick weight of members in "Security Review" and "Upstream feature flag review""

What does this MR do and why?

Closes #44 (closed)

1. Change the pick weight of :small_orange_diamond: to 0.2(Old is 0.5)
2. Add select_by_weight in JihuMemberHelper
3. Change the picking logic and add its tests
4. Validate locally.

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