Feature Request: Handle Concurrency Conflicts

[TheTedder]

Currently, we have no way of preventing or handling concurrency conflicts in the database. The easiest way to do this would be to use the value of the UpdatedAt field as a concurrency token. We would also have to add an API response (probably a 409) to any endpoints that involve updating data.

[TheTedder]

See https://www.npgsql.org/efcore/modeling/concurrency.html?tabs=data-annotations.

[zysim]

1. Will we even hit concurrerncy? I thought our transactions are atomic, so it shouldn't happen?
2. Reading both options, it seems it'd come down to whether or not we'll have columns we don't want to trigger a concurrency check. I don't think we've got any, so I'm leaning more towards the xmin option. Unless you've got any objections I'm not thinking about?
3. Setting UpdateAt as a concurrency token shouldn't block it from other future uses, right? This shouldn't be a big issue, but I'm just wondering
4. DbUpdateConcurrencyException should still trigger regardless of the method we use, right?