[VET-6222] Investigate and fix issue with special characters in questions

[SpiralP]

VET-6222 VET-6163

dataSources.query can't accept application/json; charset=utf-8, but does work with application/json:

curl ...
        -H 'content-type: application/json; charset=utf8' \
        --data-raw '{"query":"select * from PURCHASE_ORDER where PO_DATE > \'2020-04-01\' LIMIT 25","options":{"parser.sql.quoting":"NATIVE","sql.functions":"","percent.encode":true}}'
Data Source query failed: 'pilothouse-test-new-ds-154452d5-11eb-4030-858b-fdcadc384cd4': Invalid SQL syntax found. Encountered "{" at line 1, column 1.
Was expecting one of:

[SpiralP]

noting i got all these here to pass after running this (and removing the .only below)