You are actually connecting through a proxy. That proxy seems not to handle TLS properly, since you can see, that you've get some SSL_ERROR_PROTOCOL_VERSION_ALERT. So I am not sure if it will be possible to get this working behind that proxy. Please consult whoever is managing that proxy, that you are using, and just show them that above curl request. As soon as that curl is working, Kibana shouldn't have an issue anymore downloading that plugin.
Cheers,
Tim