Added Sol - An MQTT broker from scratch tutorial

[codepr]

Description

Added a comprehensive tutorial in 6 parts + bonus to build an MQTT broker from scratch in C.

Motivation and Context

The project covers a lot of interesting CS topics, like low level networks, EPOLL interface and data structures implementation.

How Has This Been Tested?

All URLs are working correctly

Types of changes

• Content Update (change which fixes an issue or updates an already existing submission)
• New Article (change which adds functionality)
• Documentation change

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have made checks to ensure URLs and other resources are valid

[tuvtran]

LGTM! Thanks for adding this.