Adding doc and tests

[matlabbe]

What this PR brings:

• Tests!
• API documentation
• Coverage report artifacts
• Doxygen artifacts
• Sphinx (ros2doc) artifacts

Breaking changes:

• USemaphore's acquire/acquireTry/release and UMutex's lock/lockTry/unlock are all now returning true or false (instead of nebulous error code), so it means if someone was calling if(mutex_.lockTry() == 0), they should now do if(mutex_.lockTry()) (inverse), meaning we could lock the mutex.
• For parameter names that have change, the downstream code would have compilation errors, so it won't compile silently like the USemaphore/UMutex breaking change.

[matlabbe]

Let's merge this as soon as possible. That will unblock testing for new features like #1721

TODO:

• revert UMutex and USemaphore breaking changes
• tag 0.23.7 before merging this (then bump minor to 0.24 version). Note that bumping minor version is usually used for new features in the database, we could make DBDriverSqlite3 still produce 0.23 database version in 0.24, for backward compatibility.