custom storage/backends

[c-antin]

Summary 💡

Any plans on supporting custom backends?
See https://github.com/go-git/go-git/tree/v5.11.0/storage
Or https://github.com/libgit2/libgit2-backends

Motivation 🔦

Use case: in-memory and/or database storage for objectDB, refDB, etc. for faster access or reduced storage footprint.