Option for simpler report output grid

[nj1973]

By default the reported output of DVT is Tabulate fancy_grid, as seen in the data_validation/result_handlers/text.py code below:

            print(
                result_df.drop(self.cols_filter_list, axis=1).to_markdown(
                    tablefmt="fancy_grid", index=False
                )

This uses complex characters that are not copy/paste friendly and also inserts a grid line between each report row. For a row validation this can add up to a lot of non-essential noise on screen.

An alternative is to use --format=text but then we gain extra columns because self.cols_filter_list columns are not dropped and lose heading underlines.

This is obviously low priority but it would be nice if could control the tablefmt value hardcoded above. Perhaps any value other than text, csv and json could be passed to to_markdown(tablefmt?

[Raniksingh]

PR #802