feature(parameter_sync): offer 2 GPU memory optimization levels in broadcasting parameters

[haolin-nju]

This PR includes:

1. offering 2 levels of GPU memory optimization level in broadcasting parameters (one-stage and two-stage)
2. supresses GPU memory utilization in broadcast (one-stage)

[adoda]

LGTM

[haolin-nju]

PTAL @adoda @charles9304

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✅ haolin-nju
❌ JiangLe9304
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