fix(docs): Type method missing from OutputParser (#972)

Added missing Type method, interface OutputParser in documentation is now identical to the /schema/output_parser.go

docs/docs/modules/model_io/output_parsers/index.mdx

@@ -22,5 +22,7 @@ type OutputParser[T any] interface {
 	ParseWithPrompt(text string, prompt PromptValue) (T, error)
 	// GetFormatInstructions returns a string describing the format of the output.
 	GetFormatInstructions() string
+	// Type returns the string type key uniquely identifying this class of parser
+	Type() string
 }
-```
+```