Add library function to lookup storage duration per channel

This sets us up to actually add configuration per channel and have all
the call sites automatically update.

Change-Id: I1c1fe11b2096d6e2bdf578902e609b718c3bcb5c
Signed-off-by: James Kuszmaul <james.kuszmaul@bluerivertech.com>
diff --git a/aos/configuration.h b/aos/configuration.h
index 06f4db4..68b3079 100644
--- a/aos/configuration.h
+++ b/aos/configuration.h
@@ -231,6 +231,10 @@
 GetSchemaDetachedBuffer(const Configuration *config,
                         std::string_view schema_type);
 
+// Returns the storage duration for a channel.
+std::chrono::nanoseconds ChannelStorageDuration(const Configuration *config,
+                                                const Channel *channel);
+
 // Adds the specified channel to the config and returns the new, merged, config.
 // The channel name is derived from the specified name, the type and schema from
 // the provided schema, the source node from the specified node, and all other