cephfs: add support for cache management callbacks

go-ceph version: v0.8.0

there is a ceph-service pod running in k8s, which use go-ceph to operate cephfs, like(create/delete dir, create/delete dir), but mds report
```
mds.sh-bs-b1-303-j14-ceph-133-2(mds.0): Client xdl-ceph-client-d6795749-z988c:xdl failing to respond to cache pressure client_id: 6704
```

I retart ceph-service , mds is ok, is it a bug in go-ceph?

The issue names go-ceph v0.8.0 and CephFS but no files, tests, or entry points. Start by reproducing the cache-pressure condition and tracing the CephFS client behavior through go-ceph; done requires determining whether go-ceph causes the failure and documenting a concrete fix or confirmed upstream cause.

Written by the indexing model from the issue text.