When creating an object through ActivityPub, two Create activities are sent

## Problem

If a `Create` activity is posted to the outbox, the `ObjectService` will create it on the corresponding container.

The problem is that, when the ObjectsWatcherMiddleware detects the object being created, it will post its own `Create` activity.

So we end up with two Create activity.

## Proposed solution

Keep somewhere in meta data the fact that the object was created through ActivityPub ?

Start by tracing the outbox handling through ObjectService and the ObjectsWatcherMiddleware, focusing on where the incoming Create activity causes object creation and where the watcher posts its own Create. Confirm the duplicate-activity path with the existing ActivityPub-related tests or reproduction described in the issue; done means one Create activity is emitted for an object created through ActivityPub.

Written by the indexing model from the issue text.