[Snaps] Incremental (diff) snapshots

[raduweiss]

The ability to create a microVM snapshot is compelling for serverless use cases. It’s also a feature ask from users.

This item tracks the capability of creating incremental (diff) snapshots. Firecracker will still only restore full snapshots, so users will need to merge incremental snapshots externally (we will provide documentation & example tooling).

[alsrdn]

We already do create incremental snapshots.

[JonathanWoollett-Light]

Still in developer preview, re-opening to indicate this.

We will move to shipped synchronously with related snapshot functionality (https://github.com/firecracker-microvm/firecracker/issues/2142, https://github.com/firecracker-microvm/firecracker/issues/1184).