Added ISO formatted strings being allowed as date inputs

[JeffersonBledsoe]

This PR is the start of using full ISO 8601 datetime strings for all submissions of dates and using the backend to friendly-format them in the sent emails.
A PR to volto-form-block needs to be made removing the formatting of dates client-side and sending them as ISO-compliant strings for this to be an effective PR.

[JeffersonBledsoe]

@cekk @pnicolli Any thoughts on this? We had a client comment on being able to use the CSV and XML data of submission in external system with full timezone strings, but still be able to nicely read the dates in any emails that are sent

[coveralls]

Pull Request Test Coverage Report for Build 7991976848

Details

• -1 of 11 (90.91%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 89.683%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/collective/volto/formsupport/restapi/services/submit_form/post.py	10	11	90.91%

Totals
Change from base Build 7919988301:	0.02%
Covered Lines:	678
Relevant Lines:	756

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💛 - Coveralls

[mamico]

@JeffersonBledsoe now the tests are green here, but your changes don't seem to be covered by the tests

[mamico]

LGTM