Add a certificate chain cache committed after chain verification in the client library

[jpraynaud]

Why

We want to update the unstable MithrilCertificateVerifier and CertificateVerifierCache implementations of the client to support a commit mechanism when the full certificate chain is validated. A first FullVerification mode of verification using the cache will verify the cryptography of the cached certificate, thus providing the same level of security than without cache.

What

Implement the new commit mechanism for the client certificate cache and the FullVerification mechanism.

How

• Update the CertificateVerifierCache trait with:
  • stage_certificate(&self, certificate_chain_validation_id: String, certificate: &CertificateMessage, expiration_at: DateTime) -> MithrilResult<()>
  • commit_staged_certificates(&self, certificate_chain_validation_id: String) -> MithrilResult<()>
  • get_certificate_by_hash(&self, certificate_hash: String) -> MithrilResult<Option<CertificateMessage>>
  • reset(&self) -> MithrilResult<()>
• Adapt the MemoryCertificateVerifierCache implementation
• Implement the FullVerification algorithm in verify_chain of the MithrilCertificateVerifier
• Adapt the ClientBuilder to configure the cache