AK2001: detect when automatically handled messages are being handled inside MessageExtractor / IMessageExtractor (Cluster.Sharding)

[Aaronontheweb]

Is your feature request related to a problem? Please describe.

Any of the messages that were previously handled manually prior to akkadotnet/akka.net#6717 should be removed from the end-user's shard message extractor, given that they're now automatically handled by Akka.Cluster itself.

Describe the solution you'd like

An Analysis rule with a DiagnositicServerity.Warning label along with a CodeFix that just removes the offending lines.

Additional context

This rule will only apply to Akka.NET versions 1.5.15 and higher.

[Aaronontheweb]

Resolved via #43