[CurveBS] Add chunkserver-level statistics and allocation limits for the curvebs capacity statistics and allocation module

[xu-chaojie]

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The current curvebs capacity statistics only consider the overall capacity of the cluster. When the capacity of a single chunkserver is insufficient, the cluster may still be unavailable. Therefore, it is necessary to add the management of the capacity of a single chunkserver and limit the space allocation when the capacity of a single chunkserver is insufficient.

[luooofan]

请问有更详细的说明嘛？ 我现在注意到 https://github.com/opencurve/curve/blob/9d48ce967a613478b0603357a80c812dc55a7d38/src/mds/topology/topology.cpp#L553-L554 以及 https://github.com/opencurve/curve/blob/9d48ce967a613478b0603357a80c812dc55a7d38/src/mds/topology/topology_stat.cpp#L39-L40 里面都有记录 chunkserver 级别的信息，在收到心跳消息的时候会进行更新

[wuhongsong]

@xu-chaojie

[xu-chaojie]

需要修改的是空间分配模块，空间分配需要考虑单个chunkserver的空间是否足够

[mikechengwei]

/assign