Always offer the install target names for nvtx3

[robertmaynard]

Description

This is required so that consumers of nvtx3 can safely use nvtx3::nvtx3-cpp consistently no matter if they are using nvtx3 from source or an installed version.

Checklist

• [x] I am familiar with the Contributing Guidelines.
• [x] New or existing tests cover these changes.
• [x] The documentation is up to date with these changes.
• [x] The cmake-format.json is up to date with these changes.

[trxcllnt]

@robertmaynard do we also want to add this to the FINAL_CODE_BLOCK of the rapids_export() calls? I recall we also needed to do this in get_arrow.cmake.

[robertmaynard]

@robertmaynard do we also want to add this to the FINAL_CODE_BLOCK of the rapids_export() calls? I recall we also needed to do this in get_arrow.cmake.

We won't need to do that with nvtx3 since rapids-cmake is generating the build and install nvtx3-config.cmake and nvtx3-targets.cmake.

[robertmaynard]

/merge