Add CSV export format options

[flowrean]

This PR adds options from csv-stringify to the extension settings, allowing users to customize the format of the generated CSV when exporting. The new settings are all in the group sqltools.csvExport, which allows to directly pass all values at once to csv-stringify. The default settings reflect the current option values.

The changes made here partly close #739. I was planning to add an option to change the CSV field separator and ended up adding some additional related options that might be useful to tweak the resulting CSV. In #739, the decimal separator is also mentioned. I don't handle this here, as it does not seem specifically related to the CSV format (could also apply to the JSON export).

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[gjsjohnmurray]

Thanks for your contribution. I have left some review comments based on code-reading (haven't done any testing).

[flowrean]

Those are valid comments. I made the changes.

[gjsjohnmurray]

Thanks!