pkg/types: add IgnoreUnknown arg and logic

This commit adds a struct type CommonArgs that is to be embedded in
every plugin's argument struct. It contains a field named
"IgnoreUnknown" which will be parsed as a boolean and can be provided to
ignore unknown arguments passed to the plugin.

plugins/ipam/host-local/config.go

@@ -35,6 +35,7 @@ type IPAMConfig struct {
 }
 
 type IPAMArgs struct {
+	types.CommonArgs
 	IP net.IP `json:"ip,omitempty"`
 }