Add very basic example for mqtt tls

[mrkeuz]

Tested on next setup:

• MicroPython 1.17 (without ca-cert's)
• Traefik Proxy 2.5 (Let's Encrypt Cert)
• Mosquitto 2.0.12

Note:

• Unable connect without ssl_params = {"server_hostname": "<addr>"}

• If keepalive = 0 (default) got MQTTException(2)

• Don't found ssl.CERT_XXX or ussl.CERT_XXX constants,
  although the constants are specified in the documentation.
  Only found in inner definitions. But didn't understand how use it outside:
  

  micropython-lib/python-stdlib/ssl/ssl.py

  Lines 5 to 7 in 3c383f6

  	for sym in "CERT_NONE", "CERT_OPTIONAL", "CERT_REQUIRED":
  	if sym not in globals():
  	globals()[sym] = object()

  Not sure if all of this is bad defaults or this behavior made by design.

[JayPalm]

Thanks for this PR! Adding the ssl_params seemed to be the magic required to get a working connection with a HiveMQ broker.

[dpgeorge]

Thanks for the PR, and sorry this took forever to review.

I tested it with mosquitto in TLS mode and it worked.