Adds support for generating a root metadata with key assignments for
the 'Root' and 'Targets' roles.
No-Docs-Update-Reason: module in early development
Change-Id: I3580dd6b2a40bdc38be8e88627685c62f2c7aa74
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/62442
Commit-Queue: Ali Zhang <alizhang@google.com>
Reviewed-by: Joe Ethier <jethier@google.com>
