Add setter with a strongly typed parameter for the transaction isolation level

[fmbenhassine]

The JobRepositoryFactoryBean should provide a setter for the transaction isolation level with a strongly typed parameter like org.springframework.transaction.annotation.Isolation.

Related to spring-projects/spring-boot#28802.

[wilkinsona]

I see you've removed the backport label, @benas. Sorry, I'm not familiar with your process here. Does that mean the change has now been backported or that you have changed your mind and it's now going to be a 5.0-only change?

[fmbenhassine]

@wilkinsona The change seems incompatible with 4.3.x, so it's in 5.0 only for now.