Add MD5, SHA1 SQL functions

`MD5/SHA1` functions are common UDFs in many SQL engines. We may support them in SQL just like `from_base64`/`to_base64`. 

A Review of Other Databases

• BigQuery : https://cloud.google.com/bigquery/docs/reference/standard-sql/functions-and-operators#md5
  • Function : MD5(String/Bytes)
  • Input : String/Bytes
  • Output : Bytes
• MySQL : https://dev.mysql.com/doc/refman/8.0/en/encryption-functions.html
  • Function : MD5(String)
  • Input : String
  • Output : String
• Oracle : https://docs.oracle.com/database/121/SQLRF/functions183.htm#SQLRF55647
  • Function : STANDARD_HASH(expr, method)
  • Input : String
  • Output : RAW
• PostgreSQL : https://www.postgresql.org/docs/current/functions-string.html 
  • Function : MD5(String)
  • Input : String
  • Output : Text
• Redshift : https://docs.aws.amazon.com/redshift/latest/dg/r_MD5.html
  • Function : MD5(String)
  • Input : String
  • Output : String