Akka.Persistence: `Akka.Persistence.Journal.AsyncWriteJournal+Resequencer` is created as a top-level `/user` actor instead of a child of the journal

[Aaronontheweb]

Version Information
Version of Akka.NET? v1.5.36 and earlier
Which Akka.NET Modules? Akka.Peristence and all implementations

Describe the bug

While reviewing some of the work we've been doing to help keep Phobos metrics clean, @object observed a massive number of Akka.Persistence.Journal.AsyncWriteJournal+Resequencer running around under the /user actor hierarchy according to Phobos metrics: petabridge/phobos-issues#86 (comment)

As it turns out, this is indeed a bug - the Resequencer is being created in the wrong place:

akka.net/src/core/Akka.Persistence/Journal/AsyncWriteJournal.cs

Line 84 in 759e93f

_resequencer = Context.System.ActorOf(Props.Create(() => new Resequencer()));

Now as for why there's such a large number of them, two theories:

1. This actor is getting abused by plugin implementations that create Resequencers on-demand and never terminate them
2. The journal actor is restarting frequently and due to this bug, the old Resequencers are never terminated.

Expected behavior

The journal should only need a single Resequencer and it should be the journal's child.

Actual behavior

YOLO