Support deleting signature

[FeynmanZhou]

Is your feature request related to a problem?

Currently, when users want to delete a signature from a signed image for some reasons, they have to use a third-party tool like ORAS to achieve it. We discussed in notaryproject/notaryproject.dev#248 and created a doc accordingly.

This process is not convenient for users because users have to install and use another tool. In general, deleting a Notary Project signature should be a fundamental capability of Notation.

What solution do you propose?

To help users conveniently delete the Notary Project signature, it would be good that Notation could support deleting a signature via a CLI command. The desired experience can be proposed in the CLI Spec if we agree this is a valid feature request.

What alternatives have you considered?

N/A

Any additional context?

No response