Feature Request: Add VDiff command flag for controlling row content in diff report

[mattlord]

Feature Description

If VDiff detects any row differences between the source and target it will provide a report which includes the rows which were different. The number of rows it will return can today be controlled using the --max-report-sample-rows flag: https://vitess.io/docs/20.0/reference/programs/vtctldclient/vtctldclient_vdiff/vtctldclient_vdiff_create/

The column values shown for the row, however, are truncated when the output is longer than 50 bytes. This can lead to situations where it's difficult, if not impossible, to identify the specific row and the actual difference(s).

We should add a flag which allows the user to control how this truncation is done: at what length, and if 0 then do not truncate at all.

Use Case(s)

User control, offering greater ability to identify the specific differences when found.