function that builds an opAttribute based on less than or equal to than logic
lte(x)
# S4 method for integer
lte(x)
# S4 method for numeric
lte(x)
# S4 method for Date
lte(x)
the value to used as a bound in the op logic. This can either be an integer, numeric, or Date data type. Different data types will return the appropriate opAttribute type