API doesn't support working with Filestore

[Arlodotexe]

Problem

There's no APIs for interacting with the Filestore in any way.

• HTTP equivalent of ipfs filestore * is missing.
• The HTTP equivalent of ipfs add --nocopy is missing.
• The HTTP equivalent of ipfs add --fscache is missing.
   

Solution

Add the missing APIs.

• Our IFileSystemApi.AddAsync API methods use an AddFileOptions parameter to specify options, which should be where --nocopy and --fscache are implemented.
• Add a new IFilestoreApi to ICoreApi in the net-ipfs-core repo and implement in IpfsClient in the net-ipfs-http-client repo. This should cover the ipfs filestore part of the API in Kubo.

See also ipfs-shipyard/net-ipfs-http-client#37

[Arlodotexe]

Closed by #41