Add support for TLS Encrypted Client Hello (ECH)

### Description

Quoted from [Wikipedia](https://en.wikipedia.org/wiki/Server_Name_Indication#Encrypted_Client_Hello):

> Encrypted Client Hello (ECH) is a [TLS 1.3](https://en.wikipedia.org/wiki/Transport_Layer_Security) protocol extension that enables encryption of the whole Client Hello message, which is sent during the early stage of TLS 1.3 negotiation.[[10]](https://en.wikipedia.org/wiki/Server_Name_Indication#cite_note-10) ECH encrypts the payload with a public key that the relying party (a web browser) needs to know in advance, which means ECH is most effective with large [CDNs](https://en.wikipedia.org/wiki/Content_delivery_network) known to browser vendors in advance.