MQTT example for SWIOT1L and a couple fixes

[CiprianRegus]

Pull Request Description

• Adding an MQTT example for the SWIOT1L project. This is an alternative to the current default firmware.
• The UART parity error flag was sometimes randomly set for the Maxim platform (probably due to noise on the UART bus). Since it was not cleared in either no-OS or the msdk, the interrupt would continuously trigger.

PR Type

• [ ] Bug fix (change that fixes an issue)
• [ ] New feature (change that adds new functionality)
• [ ] Breaking change (has dependencies in other repos or will cause CI to fail)

PR Checklist

• [ ] I have followed the Coding style guidelines
• [ ] I have performed a self-review of the changes
• [ ] I have commented my code, at least hard-to-understand parts
• [ ] I have build all projects affected by the changes in this PR
• [ ] I have tested in hardware affected projects, at the relevant boards
• [ ] I have signed off all commits from this PR
• [ ] I have updated the documentation (wiki pages, ReadMe etc), if applies

[CiprianRegus]

I'll have to update the documentation as well