Add MergeWithConfig

When dealing with logs, sometimes you need to add a new channel.  It is
easiest to just specify the json to merge in with the log file.  Make
this a function.

Change-Id: I7bd8bde72aa0103ec9c4ae0019164566787c54a2
diff --git a/aos/configuration.h b/aos/configuration.h
index bf2ec6c..9193fd5 100644
--- a/aos/configuration.h
+++ b/aos/configuration.h
@@ -32,6 +32,11 @@
     const Flatbuffer<Configuration> &config,
     const std::vector<aos::FlatbufferString<reflection::Schema>> &schemas);
 
+// Merges a configuration json snippet into the provided configuration and
+// returns the modified config.
+FlatbufferDetachedBuffer<Configuration> MergeWithConfig(
+    const Configuration *config, std::string_view json);
+
 // Returns the resolved location for a name, type, and application name. Returns
 // nullptr if none is found.
 //