Create @bitsongjs/storage package

[DavideSegullo]

We should create a new package to manage the storage, such as:

• NFT.Storage
• Pinata

[DavideSegullo]

I suggest creating a class that defines the structure of a basic provider, then each storage service implements its methods.

This allows you to also define custom classes, when those basic offers are not sufficient

[DavideSegullo]

Tasklist:

• [x] Create provider definition
• [x] Implement NFT.storage provider
• [x] Implement Pinata provider
• [x] Implement file validations
• [x] Check Pinata upload folders
• [x] Implement IPFS provider using js-ipfs -> moved to #51