CAFS friendly local mutable fuse mount

[kerneltime]

For now each new file is mapped to a new temp file that mirrors the logical fuse file hosting all IO. This needs to be replaced with a CAFS friendly staging area that chunks up files into leaf size for a given bundle config and on commit moves the files to the local blob cache to avoid extra local IO and easier parallel upload of blobs.

[kerneltime]

Child of https://github.com/oneconcern/datamon/issues/26

[fredbi]

My take on this would be a local badgerdb acting a the local key-oriented staging

[ransomw1c]

there is also filetracker to layer in-memory caching