lpad and rpad functionality

[DylanPaulusSEL]

Copy from this stackoverflow question

Looking to be able to use the lpad and rpad Postgres functions in entity core -- currently string.PadLeft() will be executed on the C# side instead of through SQL.

[roji]

@austindrenski, interested? We could also consider refactoring some of the string translators into a single class.

[austindrenski]

Sure, I can put something together tonight or tomorrow.