rgw: add tcmalloc heap profiler support via admin socket

Add RGWHeapProfilerHook to rgw_appmain.cc that registers a "heap" admin
socket command, forwarding subcommands to the shared
ceph_heap_profiler_handle_command() implementation. This enables heap
stats, start_profiler, stop_profiler, dump, release, and release rate
commands for RGW via "ceph daemon heap ".

Link radosgw against heap_profiler library, update memory-profiling
documentation, and add an integration test script.

Signed-off-by: Vinayak Tiwari <tiwarivinayak10@gmail.com>

Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Mark Kogan <31659604+mkogan1@users.noreply.github.com>