feat(replica_scheduler): introduce balance schedule algorithm

[davidcheng0922]

Which issue(s) this PR fixes:

longhorn/longhorn#10512

What this PR does / why we need it:

Introduce a balanced replica schedule method, detail in longhorn/longhorn#11922

Special notes for your reviewer:

Currently, rebalanceWeightAlpha is set to 1, which balances replicas purely based on usable storage. To make this behavior configurable, we can introduce a new setting.

Absolute size formula:

• When disk capacities differ greatly, replicas are more likely to be scheduled on larger disks.

Ratio size formula:

• Replicas are distributed more evenly among all disks, though smaller disks may reach full capacity sooner.

Hybrid formula:

• Depends on the rebalanceWeightAlpha
• hybrid = alpha*ratioImbalance + (1-alpha)*absoluteImbalance

Additional documentation or context

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