ActorTemplate: replace on_pause/on_commit/on_resume with capture_scope and minimum_scope #2102

message SnapshotConfig {
  string storage_location = 1;

  // capture_scope defines the scope captured when taking a snapshot on suspend.
  // Defaults to SNAPSHOT_SCOPE_MEMORY when unset.
  SnapshotScope capture_scope = 2;

  // minimum_scope defines the lowest state layer required for the actor
  // to resume safely. The system attempts to resume at capture_scope, but may
  // be unable to (e.g. the sandbox config changed, or the target hardware
  // can't restore the snapshot) and fall back to a lower scope. If the scope
  // it can resume at is below minimum_resume_scope, the actor enters CRASHED.
  // Must be <= capture_scope.
  // Defaults to SNAPSHOT_SCOPE_VOLUMES when unset.
  SnapshotScope minimum_scope = 3;
}

enum SnapshotScope {
  SNAPSHOT_SCOPE_UNSPECIFIED = 0;
  // Durable volumes only; the actor cold boots from its OCI image.
  SNAPSHOT_SCOPE_VOLUMES = 1;
  // Volumes plus root filesystem changes.
  SNAPSHOT_SCOPE_ROOTFS = 2;
  // Volumes, root filesystem changes, and process memory.
  SNAPSHOT_SCOPE_MEMORY = 3;
}

message  ResumeActorResponse {
  Actor actor = 1;
  bool resumed = 2;

  // The scope that we actually resumed.
  SnapshotScope scope = 3;
}