Add ADR047: Compute submission status from delivery timestamps

[theseanything]

Introduces a new architectural decision record (ADR047) outlining replacing the fixed delivery_status enum with a computed status method based on delivery timestamps allowing us to make S3 submission async.

[lfdebrux]

I'm not sure if it changes anything, but I thought I better flag it; in a recent support case (https://trello.com/c/1yMdH3Nk/2741-bounced-submission-emails-for-form-1693), we had bounce notifications that arrived 2.5 hours after the delivery notification, apparently due to issues with the receiving mail server. However, when asked, the form creator reported that the emails had been delivered.

What I think this means is that, for email submissions at least, the status can be more ambiguous than the status of delivered or bounced would necessarily suggest.

[theseanything]

I'm not sure if it changes anything, but I thought I better flag it; in a recent support case (https://trello.com/c/1yMdH3Nk/2741-bounced-submission-emails-for-form-1693), we had bounce notifications that arrived 2.5 hours after the delivery notification, apparently due to issues with the receiving mail server. However, when asked, the form creator reported that the emails had been delivered.

What I think this means is that, for email submissions at least, the status can be more ambiguous than the status of delivered or bounced would necessarily suggest.

I think that still fits the behaviours we're handling here - i.e. an asynchronous bounce, we get a delivery notification and then a bounced notification afterwards (which is the typically caused by auto-reply being configured on the mailbox).

Those submissions are eventually are represented as "bounced" (which is the same as they currently do).

You're right to flag - as we need to be aware there's latency in which we can be really confident that they are delivered. I.e. a day old "delivered" submission, is much more likely to be accurate than a few seconds old. I think this is okay, as the vast majority of async bounces happen within an hr.