client/rpc: support for mfs (files) api

[hacdias]

Checklist

• My issue is specific & actionable.
• I am not suggesting a protocol enhancement.
• I have searched on the issue tracker for my issue.

Description

Currently, our Go RPC Client does not have an interface for the ipfs files commands (MFS). A previous attempt (by me) was started many years ago (#6786) but never saw the light of day. I'm sure this is something that would come in handy for many users if we want the MFS to be more widely used (and easier to use).

[BigLep]

I'm putting this as "Best Effort" as core maintainers need to decide if they want to invest more in MFS and the requirements before putting more weight on the feature.

[hunjixin]

I don't understand why this is a priority for P3. I believe the Files interface is highly applicable for IPFS-based applications, where we don't need to concern with the underlying implementation, but rather operate it just like a regular file system.

Another point of confusion is whether the "RPC client" in the current implementation can be understood as the API for the core api, rather than the API described in the documentation. if so Is there a plan to implement an rpc client implementation that aligns with the documentation description?