[Profiler] Remove `addMemoryUsageActivity` from kineto_shim (#76678)
Summary: `addMemoryUsageActivity` is effectively the same as `addCPUActivity` except it also has `addMetadata` calls. This change generalizes `addCPUActivity` (We have to define an enum to map to `libkineto::ActivityType`) to accept arbitrary metadata strings.
Test Plan: Unit tests
Differential Revision: D36070203
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76678
Approved by: https://github.com/aaronenyeshi
