[agent] Fetch the evidences versions supported by the verifier

[ansasaki]

Description:

This is about making a request to the endpoint where the verifier provide the versions of the evidences it supports.

The agent can potentially cache the obtained information to use in the subsequent messages without having to obtain it again for each evidences capability negotiation.

The agent should use the obtained information to select the version of the supported evidences to offer during the capabilities negotiation phase.

• 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