Update RELEASE_NOTES.md for 1.5.0-alpha4 release

[Arkatufus]

1.5.0-alpha4 February 1st 2022

Version 1.5.0-alpha3 contains several bug fixes and new features to Akka.NET

• Akka.TestKit: Remove Akka.Tests.Shared.Internal dependency
• Akka.TestKit: Added ReceiveAsync feature to TestActorRef
• Akka.Stream: Fix IAsyncEnumerator.DisposeAsync bug
• Akka: Add Exception serialization support for built-in messages
• Akka: Add simple actor telemetry feature
• Akka.Streams: Move Channel stages from Alpakka to Akka.NET repo
• Akka: Set actor stash capacity to actor mailbox or dispatcher size
• Akka: Add ByteString support to copy to/from Memory and Span
• Akka: Add support for UnrestrictedStash
• Akka: Add API for UntypedActorWithStash
• Akka.Persistence.Sql.Common: Fix unhandled DbExceptions that are wrapped inside AggregateException
• Akka.Persistence.Sql: Fix persistence id publisher actor hung on failure messages
• Akka: Change default pool router supervisor strategy to Restart
• NuGet package upgrades:
  • Bump Microsoft.Data.SQLite from 6.0.10 to 7.0.2
  • Bump Google.Protobuf from 3.21.9 to 3.21.12
  • Bump Newtonsoft.Json from 9.0.1 to 13.0.1
  • Bump Microsoft.Extensions.ObjectPool from 6.0.10 to 7.0.2
  • Bump Microsoft.Extensions.DependencyInjection from 6.0.1 to 7.0.0

[Aaronontheweb]

Going forward, we should use beta designations for 1.5 - it's stable enough.

[Arkatufus]

Will do.