ENH Add ability to ignore missing fields

[lekoala]

Description

SHOW FULL FIELDS are costly queries. Maybe it's not necessary to do this on every request

Manual testing steps

Using debugbar, you can check the queries
With this new feature, this prevents all queries: SHOW FULL FIELDS IN xxx

Issues

#828

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[tractorcow]

The fix I've proposed at #831 is better since it precisely enables the check only when necessary, rather than relying on the site owner to manually enable it.

[tractorcow]

@lekoala can you let me know if you are happy for me to merge my fix over yours?

[lekoala]

@tractorcow yes please do :-) your approach is better

[tractorcow]

Fixed with #831