Change validate to validate_data variable name for Logical Type validation

- We have 2 different validation checks in Woodwork
- 1. Overall Woodwork.df initialization validation --> We validate that in index is unique, columns headers are unique, time index is certain Logical Type
- 2. Logical Type data validation --> Make sure that the underlying values are validate. For examlple, that allow non-NaN values in an EmailAddress column have an `@` symbol.
- To make this more clear internally & externally, we should change the name of the parameter **from `validation` to `validate_data` for Logical Type validation.**