Add support for SSL mutual auth (IDFGH-1111)

[rbino]

This makes it possible to port esp-mqtt mutual auth support to the idf version.

Tested and working with the esp-mqtt mutual auth example.

[rbino]

Rebased on master with the new esp_ transport prefix

[rbino]

Rebased again to remove conflicts

[david-cermak]

Hi @rbino,

This looks really good and solves some recent requests from other customers!

We have taken you PR for internal review. I added all the needed bits from esp-mqtt
(including the recent PRs from you) to make it compilable/working together, also with the 'esp_' renaming (espressif/esp-mqtt#81 is no longer necessary)
Please note that it may take some time until reviewed and gone through the internal process and pipelines.

Thank you for your contribution and taking the time with all the rebasing/updating/renaming! It is really much appreciated!
David

[rbino]

Thanks, I will close the other PR since you already adapted the changes internally.

[mahavirj]

Closing, changes are already part of esp-tls component. Thanks.