OMPT Target Offload Support (#17)

- Porting from https://github.com/ROCm/omnitrace/pull/411
- Improve OMPT support
- Add OpenMP target example to testing
- Update Timemory submodule to use ROCm/Timemory rather than NERSC/Timemory
- Update `actions/upload-artifacts` to v4
- Standardize the `cmake_minimum_required` to 3.18.4 across workflows, project, and examples
- Updated Ubuntu 20.04 workflows

.gitmodules

@@ -1,6 +1,6 @@
 [submodule "external/timemory"]
 	path = external/timemory
-	url = https://github.com/NERSC/timemory.git
+	url = https://github.com/ROCm/timemory.git
 [submodule "external/perfetto"]
 	path = external/perfetto
 	url = https://github.com/google/perfetto.git