Prevent new user assertion statuses on the same flag deleting old ones

[peggynewman]

Example situation: a user flags a record. A resolver sees the flag, acknowledges an error exists and knows why, but cannot resolve it for whatever reason (let’s say an expert need to re-det the voucher, but they won’t be at the herbarium for two months). In this case, the resolver can verify the flag with the ‘Unresolved issue, recognised by data custodian’ user assertion status. This is helpful as it provides an update to the flagger/any other user inspecting the record and indicates that something is being done about it, but keeps the flag active in the interim until it is actually resolved.

In two months’ time, the issue gets fixed, so the resolver adds another verification, this time selecting the status ‘Corrected via data refresh’. However, doing so deletes the initial verification and explanatory comment. That original comment/context is now permanently lost. This needs to be resolved so the full history of comments/statuses attached to each flag is retained.

cc @tmesaglio for testing

[adam-collins]

I expect this is a change to the biocache-service user assertion consolidation found at AssertionService.getCombinedAssertions

It requires the removal of the function's requirement and implementation for

// 2. for verified assertion (whose code == 50000), it's uniquely related to an assertion.
//    so if there's already a verification for an assertion, a newly created verification on same assertion will overwrite existing one
//    verification is unique per assertion