`gather_process_measures()` not working on macOS

### What Operating System(s) are you seeing this problem on?

macOS

### Backend.AI version

23.03.dev0

### Describe the bug

Due to the limitations of current `gather_process_measures()` implementation, `gather_process_measures()` won't work on macOS. We need to decide: are we gonna expand current implementation to also add support for LinuxKit based Docker implementation, or just drop support for per-process metric on macOS?

### To Reproduce

_No response_

### Expected Behavior

_No response_

### Anything else?

_No response_

JIRA Issue: BA-216

Start by locating the gather_process_measures() implementation and reading how it collects per-process metrics on supported platforms. Compare those assumptions with macOS and the LinuxKit-based Docker implementation described in the issue. Done means reaching and documenting a decision on whether to add macOS support or drop per-process metrics there, with the affected behavior verified.

Written by the indexing model from the issue text.