zhanjh

*Issue #, if available:* *Description of changes:* This PR is based on [aws-nitro-enclaves-image-format/pull/30](https://github.com/aws/aws-nitro-enclaves-image-format/pull/30) - Add subcommand `measure-enclave` to generate measurements without writing output enclave image file - Add subcommand `sign-pcr0`...