Add an API in ScalarUdf to get the Udf display information

Currently if users implement new UDFs or if Samza SQL implements a new system UDF, they need to manually register that UDF's information in the "listFunctions" of Samza executor. So we may need to require UDFs to provide a function of getting their "SamzaSqlUdfDisplayInfo", then Samza executor can get the UDF information from SamzaSqlApplicationConfig.udfResolver(or SamzaSqlApplicationConfig.udfMetadata) instead of registering UDFs manually.