Generalize gz vendor use and modernize CMake

[j-rivero]

Description

I was testing the use of upcoming Gazebo Ionic with current jazzy branch (it is using Gazebo Harmonic by default) and found that the use of the new vendor packages could be improved and corrected according to https://gazebosim.org/docs/ionic/ros2_gz_vendor_pkgs/#cmakelists-txt-for-building-with-gazebo-vendor-packages

I've also modernize the CMake a bit to solve problems with exporting the necessary linking.

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

I test the compilation using Gazebo Ionic in a docker container.

Checklist

• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation

[alsora]

The changes look good to me, but the CI Is failing because it can't find one of the new cmake targets

[j-rivero]

The changes look good to me, but the CI Is failing because it can't find one of the new cmake targets

Ouch sorry. It should be fixed now.

[alsora]

Thanks, there's a few linter errors, would you mind fixing them?

Then we should be good to merge