Lock persistence journal table on write

[Arkatufus]

Changes

Change journal table write transaction isolation from undefined to serializable.
This is done to prevent a racy condition in a very write heavy environment, coupled with very eager read on the database.
The explanation for this is here: https://learn.microsoft.com/en-us/sql/t-sql/statements/create-table-transact-sql-identity-property?view=sql-server-ver15#remarks
Basically, for an identity column to be guaranteed to be assigned sequential number during concurrent writes is to lock the table so that only one transaction can operate on the table at any given time.

Performance Comparison

Performance was measured on MS SQL Server, 5 runs were done on each variant and only the highest result is taken, this is to assume that the most optimal condition was used on each test.
Numbers are measured in total messages per second.

Spec	Old	New
Persist	305	307
PersistAll	1318	1355
PersistAllAsync	3130	3158
PersistAsync	1026	1052
PersistGroup10	962	1033
PersistGroup100	920	1055
PersistGroup200	986	1004
PersistGroup25	982	1009
PersistGroup50	783	777
Recovering	66507	65705
RecoveringFour	71158	69620
RecoveringTwo	55984	60593

[Aaronontheweb]

Performance results look acceptable to me - no major impact.

[Aaronontheweb]

LGTM