Sentry groups different ApiErrors w/ common stack traces together

[pjenvey]

Sentry appears to group our ApiErrors together solely by their stack trace.

This particular event shows different ApiErrors triggered from commit_batch all under the same parent event:

https://sentry.prod.mozaws.net/operations/syncstorage-prod/issues/8179009/events/

• An attempt at a conflicting write Don't emit 503 Conflict errors to sentry #614
• 8-RESOURCE_EXHAUSTED Investigate 8-RESOURCE_EXHAUSTED AnyAggregator ran out of memory #616
• 6-ALREADY_EXISTS Handle AlreadyExists in bsos errors #619

We had set the "attempt at a conflicting write" error to be ignored via Sentry, which inadvertently hid the last 2 from the dashboard completely (the ignore went away went the stack trace completely changed after the 0.3.1 deploy). (Note: We're aware of the other errors, as they were noted here: https://bugzilla.mozilla.org/show_bug.cgi?id=1623671)