Adding Plugin Interface

- Add roctracer plugins hooks
- Add Roctracer plugin environment variable
- Add the plugin class
- Add the plugin implementation

Change-Id: I12ee2e2be035abac14864764fb76837a4533cf60

plugin/exportmap

@@ -0,0 +1,7 @@
+{
+global: roctracer_plugin_initialize;
+        roctracer_plugin_finalize;
+        roctracer_plugin_write_callback_record;
+        roctracer_plugin_write_activity_records;
+local:  *;
+};