Upsert doesn't work for Oracle

[blafond]

ORM's Oracle upsert support includes the custom operation SqlAstTranslatorWithUpsert which creates a custom DeleteOrUpsertOperation (which implements SelfExecutingUpdateOperation)

We'll need to create a Reactive version of DeleteOrUpsertOperationand change ReactiveMutationExecutorSingleSelfExecuting.performReactiveSelfExecutingOperations() to check for this type.

[blafond]

Fixed as part of this PR : Upsert support for dbs #1781 for issue #1768