Backport GZ_SANITIZER variable

[scpeters]

🎉 New feature

Backport a feature to simplify the fixing of cmake deprecation warnings in CI

Summary

This backports the GZ_SANITIZER variable so that it can be used in jenkins and fix some cmake deprecation warnings.

• https://build.osrfoundation.org/job/ignition_cmake-ci_asan-main-focal-amd64/15/

CMake Deprecation Warning at cmake/GzSanitizers.cmake:58 (message):
  Ign prefixed variable [IGN_SANITIZER] is deprecated! Use [GZ_SANITIZER]
  instead!
Call Stack (most recent call first):
  cmake/GzCMake.cmake:33 (include)
  CMakeLists.txt:19 (include)

Test it

Checklist

• [X] 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)
• [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.