[agent] Implement evidences gathering and sending to the verifier

[ansasaki]

Description:

This is about implementing the evidences gathering and sending them to the verifier for the agent driven (push) attestation

• Complete description: Attestation protocol
• Enhancement: 103: Agent-driven attestation
• Project board: Agent-driven attestation

Checklist:

• Changes implemented
• Tests added
• Documentation updated
• If configuration options are modified, the templates should be updated