common/logging: Move Log::Entry declaration to a separate header

This reduces the load of requiring to include std::chrono in all files which include log.h

src/common/CMakeLists.txt

@@ -79,6 +79,7 @@ add_library(common STATIC
     logging/filter.cpp
     logging/filter.h
     logging/log.h
+    logging/log_entry.h
     logging/text_formatter.cpp
     logging/text_formatter.h
     logging/types.h