Add support for Kubo MFS

[Arlodotexe]

The problem

The Core API does not have a way to interact with MFS.

The solution

Create a new interface and the types needed for interacting with MFS via the Core API. This includes all endpoints under /api/v0/files/.

Reference:

• https://docs.ipfs.tech/concepts/file-systems/#mutable-file-system-mfs
• https://docs.ipfs.tech/reference/kubo/rpc/#api-v0-files-ls

[Derrick-]

I have this written, I'll PR soon

See also https://github.com/ipfs-shipyard/net-ipfs-http-client/issues/14