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

• [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)
• [ ] 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]

Triggered nightlies:

• Jammy
• Focal

[onurtore]

Tested locally, LGTM.