Remove submissionCreate from entity audit events

[ktuite]

Closes #1036

It used to be that entity events that were triggered by a Submission (e.g. entity create OR update) would return these objects in the details:

• sourceEvent (the actual event that caused the entity update, whether it was a submission approval, or submission creation, etc.)
• submission (the Submission object, but only if a Submission was part of the event AND the Submission was not deleted)
• a submissionCreate object for the Submission (if a Submission was part of the event) that had enough historical information including the creation time and instance ID to describe the Submission even if it was deleted.

Now, entity audits (accessed via /projects/.../datasets/.../entities/[uuid]/audits) have details.source. This looks like

• source: { submission, event } (for events like create and update that were triggered by a submission)
• source: {} (empty source object for events triggered through the API)

This now matches the structure of source returned for Entity Versions.

What has been done to verify that this works as intended?

Tests

Why is this the best possible solution? Were any other approaches considered?

We've been discussing this for a while.

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

Does this change require updates to the API documentation? If so, please update docs/api.md as part of this PR.

There's a small documentation change included in this PR showing that an entityVersion source no longer contains submissionCreate. But we don't document the details of specific audit events, so the main change in this PR doesn't need a docs change.

It is super important for us making changes on frontend, though, so I'm trying to document it here 😅

Before submitting this PR, please make sure you have:

• run make test-full and confirmed all checks still pass OR confirm CircleCI build passes
• verified that any code from external sources are properly credited in comments or that everything is internally sourced

[matthew-white]

Just an idea (and maybe for a future PR), but what do you think about grouping sourceEvent and submission in a source object that's similar to the source object on the entity version response? I.e., details: { source: { event, submission } }

const details = mergeLeft(audit.details, sourceEvent
  .map(event => ({ source: { event, submission } }))
  .orElse(undefined));

[ktuite]

This is worth thinking about when we get to getodk/central#583, yes.

[ktuite]

Maybe this is worth doing now. I hadn't looked closely at the entity versions, but I don't like that this is called details.sourceEvent and details.submission but an entity version has source.event and source.submission.