feat build: fix jemalloc memory profile running

Try to enable jemalloc memory profiling using guide: [memory_profile_running_service.md](https://github.com/userver-framework/userver/blob/develop/scripts/docs/en/userver/memory_profile_running_service.md)

There are two errors:

- setting `USERVER_FEATURE_JEMALLOC=ON` doesn't cause `USERVER_FEATURE_JEMALLOC_ENABLED` macros being defined for handler source file: https://github.com/userver-framework/userver/blob/develop/core/src/server/handlers/jemalloc.cpp#L51 -> handler response "jemalloc is not available" even with `USERVER_FEATURE_JEMALLOC`
- Function name `IsProfilingEnabledViaEnv` has been changed

Tests: протестировано CI

Pull Request resolved: #840
commit_hash:14a4fc434ae9835d37d89fed63935f9978cf7fa1

Author: Aleksey Ignatiev

core/CMakeLists.txt

@@ -93,7 +93,7 @@ endif()
 # https://github.com/jemalloc/jemalloc/issues/820
 if (USERVER_FEATURE_JEMALLOC AND NOT USERVER_SANITIZE AND NOT CMAKE_SYSTEM_NAME MATCHES "Darwin")
   set_property(
-    SOURCE ${CMAKE_CURRENT_SOURCE_DIR}/src/utils/jemalloc.cpp
+    SOURCE ${CMAKE_CURRENT_SOURCE_DIR}/src/utils/jemalloc.cpp ${CMAKE_CURRENT_SOURCE_DIR}/src/server/handlers/jemalloc.cpp
     APPEND PROPERTY COMPILE_FLAGS -DUSERVER_FEATURE_JEMALLOC_ENABLED=1
   )
 endif()

core/src/server/handlers/jemalloc.cpp

@@ -60,7 +60,7 @@ std::string Jemalloc::HandleRequestThrow(const http::HttpRequest& request, reque
         case Command::kStat:
             return utils::jemalloc::Stats();
         case Command::kEnable:
-            if (!utils::jemalloc::IsProfilingEnbledViaEnv()) {
+            if (!utils::jemalloc::IsProfilingEnabledViaEnv()) {
                 request.SetResponseStatus(server::http::HttpStatus::kServiceUnavailable);
                 return "'jemalloc' profiling is not available because the service was not started with a 'MALLOC_CONF' "
                        "environment variable that contain 'prof:true'";