Resolve "CMake config/target install dir"

What does this MR do?

Uses DUNE_INSTALL_LIBDIR for installing config and target files.

Is there something that needs to be double checked?

I have no CentOS CI to check this, @liam.keegan does this solve the issue?

Can this MR be accepted?

• I've read contribution guide
• Implemented
• Added/Updated tests
• Added/Updated documentation
• Pipelines passing

• Delete branch option set
• Fast-forwaded git merge is possible
• Added entry to CHANGELOG.md

Related issues

Closes #63 (closed)