python bindings: get version from package.xml

[scpeters]

🎉 New feature

Similar to gazebosim/gz-math#642 using gazebosim/gz-cmake#456 from gz-cmake 4.1.0

Summary

When building python bindings separately from the main library, the major version of gz-transport has been hard-coded, but this changes it to parse the version number from the package.xml file in this repository using a gz-cmake feature added in gazebosim/gz-cmake#456 and released in 4.1.0. We could also consider using this feature in the root CMakeLists.txt file, but for now it is just used when building python bindings separately from the main library.

Test it

1. Configure the python folder:

cd python
mkdir build
cd build
cmake ..

2. Verify that it found gz-transport14

-- Looking for gz-transport14 -- found version 14.0.0

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[caguero]

Works for me!