Add GREATEST_IGNORE_NULLS to snowflake.functions.ts (#758)

See
https://docs.snowflake.com/en/sql-reference/functions/greatest_ignore_nulls

Let me know if I am missing some steps. Thank you!

Author: nene

src/languages/snowflake/snowflake.functions.ts

@@ -200,6 +200,7 @@ export const functions: string[] = [
   'GET_STAGE_LOCATION',
   'GETBIT',
   'GREATEST',
+  'GREATEST_IGNORE_NULLS',
   'GROUPING',
   'GROUPING_ID',
   'HASH',