Added DbBatch support

[jarlebh]

Fixes #147

Changes

Added new PostgreDbBatchSqlJournal that uses DbBatch when persisting, this increases performane of PersistAll x 20, also added .net6 support as this is needed to get right version of DbBatch in .net6

Checklist

For significant changes, please ensure that the following have been completed (delete if not relevant):

• [ ] This change follows the Akka.NET API Compatibility Guidelines.
• [ ] This change follows the Akka.NET Wire Compatibility Guidelines.
• [ ] I have reviewed my own pull request.
• [ ] Design discussion issue #
• [ ] Changes in public API reviewed, if any.
• [ ] I have added website documentation for this feature.

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[Aaronontheweb]

cc @CumpsD any thoughts on this?

[CumpsD]

cc @CumpsD any thoughts on this?

If it passes the test, I'm all for it, since it is opt-in anyway via HOCON

I do have to mention I am not busy with akka.net on postgresql (or akka.net in general) right now due to lack of time