Persist submitting user metadata

[sc15zs]

Ticket:
https://dluhcdigital.atlassian.net/browse/FMD-251

Description:
On submission passes user's account_id and email address to data-store/ingest.

DEBUG_USER_ACCOUNT_ID is added to config/envs/development.py to be able to test locally.

[Joel-Pearce]

I suggest writing a unit test to assert that the metadata is successfully extracted from the g class and sent to the backend. It can be written with a mocked user, much as we have done for our authorisation tests.

[sc15zs]

I suggest writing a unit test to assert that the metadata is successfully extracted from the g class and sent to the backend. It can be written with a mocked user, much as we have done for our authorisation tests.

As discussed, there's not much we could test in submit, so there are no tests here.
Unit test has been added to the data-store to make sure submitted values are successfully saved on Submission model.

test has been added