Add COSE support

[SteveLasker]

A prototype of notation cose support has been completed.

This tracks:

• [x] Complete remote signing support: veraison/go-cose #9
• [ ] Notary Spec support of COSE #48
• [x] Add support for COSE, through the veraison/go-cose project

Other tasks:

• [ ] #287
• [ ] #288
• [ ] #289
• [ ] #290
• [ ] #291
• [ ] #292
• [ ] Refactor code to support multiple envelopes

[shizhMSFT]

The COSE support should be through notation-core-go, where notation-core-go implements COSE support through the veraison/go-cose project.