message: Replace fizz server cert with leaf cert returned from verification
  Summary: Added code to return the leaf cert after successfully verification of the server cert. The returned cert is then used for replacing the server cert.
diff: @@ -15,9 +15,10 @@ class TestCertificateVerifier : public fizz::CertificateVerifier {
  public:
  ~TestCertificateVerifier() override = default;
  - void verify(const std::vector<std::shared_ptr<const fizz::PeerCert>>&)
  + std::shared_ptr<const folly::AsyncTransportCertificate> verify(
  + const std::vector<std::shared_ptr<const fizz::PeerCert>>& certs)
  const override {
  - return;
  + return certs.front();
  }
  [[nodiscard]] std::vector<fizz::Extension> getCertificateRequestExtensions()
  