CurveBS: All chunkservers share walpool

[ilixiaocui]

Is your feature request related to a problem? (你需要的功能是否与某个问题有关?)
The files used by wal in raft are obtained from the file pool.
The current design is that each chunkserver has its own file pool. We hope to provide a way that all chunkservers on a machine can share a file pool. Facilitates the sharing of space.

Describe the solution you'd like (描述你期望的解决方法)
Provides a process-safe FilePool

curve/src/chunkserver/datastore/file_pool.h

Line 137 in 00bf32f

class CURVE_CACHELINE_ALIGNMENT FilePool {

Describe alternatives you've considered (描述你想到的折衷方案)

Additional context/screenshots (更多上下文/截图)

[yubindy]

This means that the walpool and chunkfilepool are separated, a chunkserver occupies a chunkfile, and this physical machine exclusively occupies the walpool, so the filepool of this part of the walpool is obtained from a separate chunkserver, right? What I understand is

[ilixiaocui]

This means that the walpool and chunkfilepool are separated, a chunkserver occupies a chunkfile, and this physical machine exclusively occupies the walpool, so the filepool of this part of the walpool is obtained from a separate chunkserver, right? What I understand is

walpool and chunkfilepool now support separate configuration，as follows in conf/chunkserver.conf

Currently:
chunkserver1 walpool chunkfilepool
chunkserver2 walpool chunkfilepool

We want all chunkserver shares walpool