Install executable to unversioned folder

[scpeters]

🎉 New feature

Follow up to gazebo-tooling/release-tools#1244.

Summary

We removed version numbers from package names in many places as part of gazebo-tooling/release-tools#1244, prioritizing the places that most affect users. While reviewing gazebo-release/sdformat16-release#5, I realized that we can install the executable commands to unversioned folders as well (see gazebosim/sdformat#1569), which should make our packaging metadata easier to maintain.

Test it

I will open a PR to the release repository and build a nightly deb from this branch for testing. Tested with gazebo-release/gz-msgs12-release#3

• https://build.osrfoundation.org/job/gz-msgs12-debbuilder/86/

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)
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