after use curvebs for the backend of curvefs，a unified name needed

[wuhongsong]

Is your feature request related to a problem? (你需要的功能是否与某个问题有关?)

Regardless of whether the backend is s3, or bs, we now use a unified cache layer(https://github.com/opencurve/curve/tree/fs_curvebs_storage_support) ,so we need a unified name,

for example: S3ChunkInfo maybe replaced by ChunkInfo(or other name)

Describe the solution you'd like (描述你期望的解决方法)

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)

[infdahai]

Let me have a try.

[wuhongsong]

Let me have a try.

yeap, lets do it.

[Cyber-SiKu]

@infdahai Have you encountered any difficulties?

[infdahai]

@Cyber-SiKu I will propose a draft pr in these few days.

[caoxianfei1]

@Cyber-SiKu I will propose a draft pr in these few days.

ok