Review requested of String Handling Doc

Hi,

I have created a [document](https://github.com/GoogleCloudPlatform/professional-services-data-validator/blob/issue-1368-fixed-length-pks/docs/internal/strings.md) about how DVT handles strings and changes that I recommend.

Can we have a robust discussion and hear your thoughts ?

Not all issues are high priority - so something like alternate encoding for DB2 may be low priority until a customer needs it.

Thanks.

Sundar Mudupalli