tracing: Add init option to avoid linking system consumer

Today when using perfetto::Tracing::Initialize() with the system
backend, both the producer and the consumer side of the ipcs are linked
in, even though most perfetto users will not likely use the consumer
side.

The consumer side implementation is responsible for a large portion of
the statically linked binary size (~100Kbytes out of ~700kBytes, thanks
rzuklie@google.com for finding that out!).

This commit adds an option to perfetto::Tracing::Initialize to avoid
initializing the consumer side of the system backend.

Change-Id: I17a72f4864c6c300a6a734f93b349e6d020f1967
diff --git a/CHANGELOG b/CHANGELOG
index 36e88af..ef4b9fc 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -15,6 +15,8 @@
       been deprecated in favor of this new functionality.
     * Deprecated the PERFETTO_COMPONENT_EXPORT macro in favor of
       PERFETTO_DEFINE_CATEGORIES_IN_NAMESPACE_WITH_ATTRS.
+    * Added TracingInitArgs::enable_system_consumer configuration option, that
+      allows the linker to discard the consumer IPC, if not required.
 
 
 v31.0 - 2022-11-10: