Consider a 'check' subcommand

[chevdor]

This remains to be spec'ed but the main idea is to allow used to check a given "srtool result" coming in the form of a json file.

The json file needs to contains all the parameters for the user to reproduce the same build without having to care much about the flags and options.

At the end of the build, the output is similar to a regular build, with, in addition, a comparison of the hashes.

[chevdor]

Here is the list of info required for a run and a check:

run

• image
• tag-version: fully specified tag, 1.53.0 is not enough, we need the full 1.53.0-0.9.15 to ensure we pick the right image and not blindly the last `1.53.0
• runtime_dir
• (package) (having the runtime_dir), we should not need the package

check

• proposal hash
• blake2_256
• image digest

[chevdor]

See #13