feat: another way to get heap profile

[vagetablechicken]

rdsn/src/dist/http/pprof_http_service.cpp

Lines 327 to 335 in 4167057

	static bool get_heap_profile(std::string &result)
	{
	if (!is_heap_profile_enabled()) {
	result = "no TCMALLOC_SAMPLE_PARAMETER in env";
	return false;
	}
	MallocExtension::instance()->GetHeapSample(&result);
	return true;
	}

We use GetHeapSample() which means we must run servers with sampling turned on(set TCMALLOC_SAMPLE_PARAMETER). If we want to get heap profile, we must restart the server. It's completely unnecessary.

https://gperftools.github.io/gperftools/pprof_remote_servers.html says,
The other way is to call HeapProfileStart(filename) (from heap-profiler.h), continue to do work, and then, some number of seconds later, call GetHeapProfile() (followed by HeapProfilerStop()). The server can send the output of GetHeapProfile back as the HTTP response to pprof. (Note you must free() this data after using it.) This is similar to how profile requests are handled, below. This technique does not require the application to run with sampling turned on.

We can consult the implement in Doris for more details.

@hycdong @levy5307