[#174] Add fallback path to search

Fallback path to search is needed because
some software may keep FileName attribute
and ignore FilePath attribute during file
upload. Therefore, if this feature is
enabled under certain conditions (for more
information, see gate-configuration.md) a
search will be performed for the FileName
attribute.

Signed-off-by: Roman Loginov <r.loginov@yadro.com>

cmd/http-gw/settings.go

@@ -164,6 +164,9 @@ const (
 	cfgMultinetFallbackDelay = "multinet.fallback_delay"
 	cfgMultinetSubnets       = "multinet.subnets"
 
+	// Feature.
+	cfgFeaturesEnableFilepathFallback = "features.enable_filepath_fallback"
+
 	// Command line args.
 	cmdHelp          = "help"
 	cmdVersion       = "version"