[Spec] CLI Cmds for Trust Policy Management

[yizha1]

Summary

Define the CLI specification for Trust Policy management

Intended Outcome

The specification PR is reviewed, merged, and stored under https://github.com/notaryproject/notation/tree/main/specs/commandline

Additional context

[iamsamirzon]

@toddysm , @vaninrao10 , @FeynmanZhou , @yizha1 - Based on RC-2 discussion in today's Notary v2 meeting, I am pushing back this item from the RC-2 roadmap into the backlog.