Refactorization of supported platforms sections

[FranFin]

TODO:

• Add a section in Overview which is: "micro-ROS modules for external platforms"
• Add STM32CubeMX to external build systems in Concepts page
• Change boards organization in Supprted HW page in Overview page and add transport/RTOS/external BS info
• Remove Transports page and absorb info into HW page
• Reorganize tutorial sections
• Update Users, collaborators etc section w/ new users

[FranFin]

@pablogs9 As soon as we have some spare time.