CMake macro to find the assimp library

[luca-della-vedova]

🎉 New feature

Summary

This PR adds support to gz_find_package for finding the assimp package including the ability to specify a version.

Test it

It can be tested with the upstream PR in gz-common, try to build it with and without this branch and check that it fails without.

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.

[chapulina]

Works for me locally on Linux. On Focal it detects a version below 5.2.0 and on Jammy it's above. We could try out macOS and Windows with some custom branches before merging, but since this change is quite isolated, we're close to feature freeze, and it targets an unstable branch, I think it's worth merging it and we can iterate on future PRs if needed.

[chapulina]

Triggered nightlies:

• Jammy
• Focal

[onurtore]

Tested locally, LGTM.