Exclude OGRE2 Overlay using a CMake argument (gz-rendering10) (backport #1177)

[mergify]

🎉 New feature

Twin of #1175, related to OGRECave/ogre-next#541 should help with conda-forge/gz-rendering-feedstock#42 (comment).

Summary

This is mainly a port of #1175 to be activated under the parameter USE_OGRE2_OVERLAY enabled by default to keep current ABI stable.

Test

Testing on Mac with the option disabled in https://build.osrfoundation.org/job/gz_rendering-ci-pr_any-homebrew-amd64/417/.

Checklist

• Signed all commits for DCO
• Was GenAI used to generate this PR

Generated-by: Sonnet 4.0

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

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This is an automatic backport of pull request #1177 done by Mergify.

[mergify]

Cherry-pick of bb0e866 has failed:

On branch mergify/bp/gz-rendering10/pr-1177
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Changes to be committed:
	modified:   CMakeLists.txt
	modified:   include/gz/rendering/config.hh.in
	modified:   ogre2/include/gz/rendering/ogre2/Ogre2Includes.hh
	modified:   ogre2/include/gz/rendering/ogre2/Ogre2RenderEngine.hh
	modified:   ogre2/src/Ogre2RenderEngine.cc
	modified:   ogre2/src/Ogre2Scene.cc

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   Changelog.md

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