New HTTP endpoint for creating verifiable credentials

Until now the signer was only able to create Verifiable Presentations or add proofs to given credentials or presentations. This issue is for creating new dedicated endpoint for issuing Verifiable Credentials.

Subtasks to be implemented with this issue:

• HTTP endpoint for generating VC from random JSON (credentialSubject)
• Support the creation of multiple proofs (signatures) in a VC
• Support verification of multiple proofs in a VC
• Update integration tests to include cases for new functionalities
• Update healthcheck endpoints to include service version