feat: implement attestation micro service

Description

Implementation of Attestation manager, same as the Connection manager it's closed behind the gateway.

Gateway api now supports:

1. creating credential definition
2. issue credential
3. list all credentials
4. list all offers
5. accept an offer

Related issues

#11 (closed)

Testing

Checklist

• I have updated the documentation (if necessary)
• I have added unit tests for new functionality (if applicable)
• My code follows the style guidelines of this project
• I have tested this code on my local machine before submitting this MR

Reviewers

Additional Notes

No additional notes.

Closes #9 (closed)