Add helper methods for sql plugin registeration (cadence-workflow#4024)

common/persistence/sql/store.go

@@ -37,6 +37,19 @@ func RegisterPlugin(pluginName string, plugin sqlplugin.Plugin) {
 	supportedPlugins[pluginName] = plugin
 }
 
+// RegisterPluginIfNotExists will register a SQL plugin only if a plugin with same name has not already been registered
+func RegisterPluginIfNotExists(pluginName string, plugin sqlplugin.Plugin) {
+	if _, ok := supportedPlugins[pluginName]; !ok {
+		supportedPlugins[pluginName] = plugin
+	}
+}
+
+// PluginRegistered returns true if plugin with given name has been registered, false otherwise
+func PluginRegistered(pluginName string) bool {
+	_, ok := supportedPlugins[pluginName]
+	return ok
+}
+
 // NewSQLDB creates a returns a reference to a logical connection to the
 // underlying SQL database. The returned object is to tied to a single
 // SQL database and the object can be used to perform CRUD operations on