Support for GCP Cloud storage

[raiyankamal]

I'm using GCP for a few projects and would like to see support for Cloud Storage in Flan. I'm hoping to find some time to work on this myself. Opening the issue here now for keeping track and just in case someone else also wants to contribute.

[hhaidar]

Oclif has a "plugins plugin" but I'm not sure it would be particularly useful for a generic storage API.

I'm going to think about it more but please let me know if you already have something in mind. Supporting S3, Cloud Storage, Azure, etc and making it easy for people to extend would be awesome.