Allow freezing the micro-ROS package versions

I got back to working on my project after a couple of months. When I tried to build it, it no longer compiled because the library builder pulled newer version of micro-ROS packages that contained API changes that were not compatible with my code.

I think this library should either be tied to specific versions of the packages and have a library auto-update workflow (similar to the on [micro_ros_arduino](https://github.com/micro-ROS/micro_ros_arduino)) or allow the user to specify the versions.

Start by locating the library builder and the code that resolves micro-ROS package versions. Determine whether the project should pin versions, provide user-selected versions, or support an update workflow; the issue does not decide between these options. Done requires builds to avoid unexpected incompatible package updates.

Written by the indexing model from the issue text.