Fix volto.formsupport path to not alter returned data on POST.

[cekk]

The problem was that with enabled "store data" flag, the patch changed the POST response data structure, and the frontend cannot read submitted data for the thank-you page:

Standard response:

{
 "data": {....}
}

Response with store data flag:

{
  "data": {
    "form_data": {...}
}

With this pr we don't change where the data is stored, so frontend will always get it.

This is related to italia/design-comuni-plone-theme#192

[coveralls]

Pull Request Test Coverage Report for Build 12258692351

Details

• 7 of 7 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 55.995%

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Totals
Change from base Build 12177079948:	0.1%
Covered Lines:	495
Relevant Lines:	884

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💛 - Coveralls