Add colcon.pkg with gz-cmake4 dependency

[scpeters]

🦟 Bug fix

Fixes colcon build ordering since #136 was merged

Summary

Since https://github.com/gazebosim/gz-tools/pull/128, gz-tools2 supports building with either gz-cmake3 or gz-cmake4, and colcon was correctly identifying the dependency relationship due to the cmake find_package calls. A package.xml was added in #136 with a build_depend only on gz-cmake3, which now breaks the build-from-source order for Ionic workspaces that include gz-tools2:

• https://build.osrfoundation.org/view/gz-ionic/job/sdformat-main-win/43/

Starting >>> gz-cmake4
Starting >>> gz-tools2
--- output: gz-tools2
-- Selecting Windows SDK version 10.0.19041.0 to target Windows 10.0.20348.
-- The C compiler identification is MSVC 19.29.30148.0
-- The CXX compiler identification is MSVC 19.29.30148.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/VC/Tools/MSVC/14.29.30133/bin/Hostx64/x64/cl.exe - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/VC/Tools/MSVC/14.29.30133/bin/Hostx64/x64/cl.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
CMake Error at CMakeLists.txt:19 (message):
  Could not find either gz-cmake3 or gz-cmake4

-- Configuring incomplete, errors occurred!

This pull request adds a colcon.pkg file with an explicit dependency on gz-cmake4 to fix the build order

• test with this branch: https://build.osrfoundation.org/view/gz-ionic/job/sdformat-main-win/45/

Alternatives considered

• Use the colcon.pkg to force the build type back to cmake: https://github.com/gazebosim/gz-tools/commit/f18e5846887f2e290abcbc9f5ae6e0e8fa2aed42. This also fixes the build (), but it has more side-effects that just adding gz-cmake4 as a dependency.
• Add <member_of_group>gz-cmake</member_of_group> to the package.xml file in gz-cmake3 and gz-cmake4 and a <group_depend>gz-cmake</group_depend> tag in downstream package.xml files (thanks to @cottsay for the suggestion). This is more elegant but requires more coordination between packages, while this colcon.pkg change can fix CI now.

Checklist

• [X] Signed all commits for DCO
• [ ] Added tests
• [ ] Updated documentation (as needed)
• [ ] Updated migration guide (as needed)
• [ ] Consider updating Python bindings (if the library has them)
• [X] codecheck passed (See contributing)
• [X] 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.