Report whether this API can replace its own container, and what it would cost.

Read-only and never raises: a daemon that cannot be reached, a container that cannot be placed and a registry that cannot be read are all reported as can_upgrade false with a blocked_reason, because the caller of a destructive action needs a reason far more than it needs a 500.

Returns: Dictionary with image_ref, current_digest, available_digest, up_to_date, the pinning verdict (pinned / pinned_reason / override_file), the compose project, working dir and config files, running_executors and running_bots, and can_upgrade with its blocked_reason (None only when the upgrade may be started).