[improve][client] Add TLSv1.3 support

[ciuncan]

Fixes #172

Motivation

We've met this issue with a customer, whose network does deep packet inspection and somehow prevents TLSv1.2 connections to successfully do handshake. Other clients such as Java/Rust works just fine as they are able to connect with TLSv1.3. Since TLSv1.2 usage is hardcoded in CPP client (and by extension Python client), pulsar connection was no longer possible from there. I've opened a PR and would be happy to get it evaluated to be incorporated in pulsar-client (we use python package).

Modifications

The asio SSL context is now constructed with ASIO::ssl::context::sslv23_client instead of ASIO::ssl::context::tlsv12_client, and with default_workarounds | no_sslv2 | no_sslv3 |no_tlsv1 | no_tlsv1_1 options, which excludes unsafe versions and leaves only TLSv1.2 and TLSv1.3. I've tested this connection on the network and it worked fine.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

• Added TLS handshake tests (TlsNegotiationTest.cc) that will build a mock server that will either accept only TLSv1.2 and TLSv1.3
• The updated client TLS connection code is tested against both protocol versions

Documentation

• doc-required
  (Your PR needs to update docs and you will update later)

• doc-not-needed
  The change is transparent to user. It will enable the clients to be able to use TLSv1.3 automatically.

• doc
  (Your PR contains doc changes)

• doc-complete
  (Docs have been already added)

[BewareMyPower]

Thanks for your contribution, could you fix the format error?

[ciuncan]

Thanks for your contribution, could you fix the format error?

Reformatted. 👌