Add "Created" as additional (optional) parameter for post_documents (#965)

* Added "created" as optional parameter for post_documents.

* Fixed Conflict

* After Black Reformatting

* Run "add-trailing-comma"

* The right order between black and trailing comma is important....

* Added required=False

* Adds unit test for optional created in document api POST

* Fixes adding of settings override

* And a mis-added print, sigh

Co-authored-by: Philipp <philipp@invalid.invalid>
Co-authored-by: Trenton Holmes <holmes.trenton@gmail.com>

docs/api.rst

@@ -240,11 +240,13 @@ be instructed to consume the document from there.
 The endpoint supports the following optional form fields:
 
 *   ``title``: Specify a title that the consumer should use for the document.
+*   ``created``: Specify a DateTime where the document was created (e.g. "2016-04-19" or "2016-04-19 06:15:00+02:00").
 *   ``correspondent``: Specify the ID of a correspondent that the consumer should use for the document.
 *   ``document_type``: Similar to correspondent.
 *   ``tags``: Similar to correspondent. Specify this multiple times to have multiple tags added
     to the document.
 
+
 The endpoint will immediately return "OK" if the document consumption process
 was started successfully. No additional status information about the consumption
 process itself is available, since that happens in a different process.