Add smaps and proc_status memory usage services

[gaber]

For context: I've been looking for ways to help applications reduce memory usage. Sometimes that means helping teams find opportunities to make greater use of shared memory. So I went looking for ways to quantify that benefit, which led me to reading proportional set size (PSS) from /proc/self/smaps_rollup.

Add two new services under src/services/memusage/:

• smaps: records RSS, PSS, and shared/private clean/dirty memory from /proc/self/smaps_rollup.
• proc_status: records virtual memory, RSS, swap, and hugetlb usage from /proc/self/status, resetting the kernel's RSS high-water mark via /proc/self/clear_refs after each snapshot (which can help uncover regions with high but short-lived usage).

Both implementations drew heavy inspiration from the existing memstat service (src/services/memusage/MemStatService.cpp), and since these new services also each read memory usage info from a file in /proc I put them in that same memusage subdirectory as a starting point. Happy to move, rename, refactor anything you want changed!

Also:

• formatted both new files with clang-format;
• added a section describing each service in doc/sphinx/services.rst;
• and added a test for each service in test/ci_app_tests/test_linux_services.py.

[daboehme]

Nice, thanks @gaber!

This is pretty much how I would have written. I'm happy to merge it.

One more thing we can do is add some ConfigManager option specs to builtin_gotcha_option_specs in src/caliper/controllers/controllers.cpp so we can use these services in built-in recipes like runtime-report. This can be added later though.