DoctrineOutboxRepository reserved words escaping

[lavernyer]

DoctrineOutboxRepository and some other Doctrine specific EventSauce classes are using backticks in sql statements. Postgresql doesn't support it, instead double quotes should be used.

db_1   [590] ERROR:  syntax error at or near "\`" at character 27
db_1   [590] STATEMENT:  INSERT INTO event_outbox (`payload`) VALUES ($1)