Save only one original definition for TestJob

Closes #644

This reduces the disk space used by TestJob table by approximately 50%. Save what used to be saved in the original_definition column in to the definition column and leave the original_definition as empty string.

The definition and original_definition is almost always the same but definition field did not have comments as they don't survive back and forth loading and dumping. One extremely rare edge case was if the TestJob was resubmitted through the web UI a "job.original" key would be saved in the job definition dictionary that would not be present in original definition. However, this value is never ever referenced again. In the future it would be better to use a nullable column to provide integrity and fast lookups.

This is backwards and blue-green migration compatible with dispatchers because the internal API endpoint used by dispatchers reads the definition field.

In the future migration that would remove the original_definition column it would be good to update the definition columns with the values from original_definition if the original_definition column was not empty to preserve comments in the definition YAML.