Support submitting job definition xml to start a job

Currently users can start a job by passing the job id and job parameters. It's also desirable to be able to pass the job definition xml itself to start a job, either by uploading a job xml file, or by passing the job xml content. In this case, the job xml may not be saved by the batch container, since it's not part of the deployment.

There are certain limitations to this way of starting a job execution. For instance, all referenced batch artifact classes must already be part of the deployed app.

Consider uploading job xml files (preferrably multiple job xml files because there are job definition inheritance with parent and child job xml files), for example,

curl -F "jobXmlFiles[]=@job1.xml" -F "jobXmlFiles[]=@job2.xml"