Add better error messages for Unsupported fake_update types

[rwnx]

I dont have a good solution for finding the exact problem but i think this error message will make a lot more sense!

the error looks something like this:

❯ pynonymizer -i tests_integration/mysql/sakila.sql.gz -o out.sql -s tests_integration/mysql/sakila.yml
There was an error while parsing the strategyfile. Unknown fake type: name_email
 This happens when an fake_update column strategy is used with a generator that doesn't exist.
You can only use data types that Faker supports.
See https://github.com/rwnx/pynonymizer/blob/master/doc/strategyfiles.md#column-strategy-fake_update for usage information.

[rwnx]

This should help with #133.