Adds an empty UpdateBundle class. It is used by the "Update
Manager" to parse, verify and provide access to a staged firmware
update bundle.
Bug: 456
Change-Id: I2df3e784ef50545f9066d4c1146f2558445ff5c8
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/58043
Reviewed-by: Ewout van Bekkum <ewout@google.com>
Reviewed-by: David Rogers <davidrogers@google.com>
Reviewed-by: Ali Zhang <alizhang@google.com>
Commit-Queue: Yecheng Zhao <zyecheng@google.com>