Support Async Datastores

[aschmahmann]

Part of implementing ipfs/kubo#6775.

There are three places pinning requires ensuring that data is stored on disk:

1. Ensure data that is requested to be pinned is on disk before adding a new pin
2. Ensure new pinned merkledag is on disk before storing a pointer to the root
3. Ensure the pointer to the root is on disk before returning to the user

[aschmahmann]

oops sent to wrong fork, sorry about that.

[MichaelMure]

I'm going to disable issues and PR here just to be sure. Otherwise, you can also ask the github support to disconnect ipfs/go-ipfs-pinner from this repo.