Use ExitStatus as parameter for Flowbuilder.on() method

Hello,

Expected Behavior

In this code

new JobBuilder("MY_JOB_NAME", jobRepository)
  ...
  .on(ExitStatus.COMPLETED.getExitCode()).to(myNextStep)
  ...
  .build(); 

add the possibility to use directly a ExitStatus type, to have:

new JobBuilder("MY_JOB_NAME", jobRepository)
  ...
  .on(ExitStatus.COMPLETED).to(myNextStep)
  ...
  .build(); 

Context

This is just a simply to use this Spring Batch class in a way that is consistent with the class Flowbuilder.

Thank you.

Start at the FlowBuilder.on() API and inspect how it currently accepts an exit-code string and how ExitStatus is represented. Add support for the ExitStatus form shown in the issue, then verify that both invocation styles build the expected flow and that the existing string form remains supported.