feat: CIM-87 - Add Comms API Identity Verification spec

[smelles]

As part of the launch for Password-less Pilot, it is necessary to release our documentation and API specification publicly on the Twilio website. This PR adds the OpenAPI specification that we are using in our project in order to generate API docs for our product.

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

If you have questions, please file a support ticket, or create a GitHub Issue in this repository.