fail dsl processing if config is already managed by another seed job

[jpederzolli]

This PR results in DSL processing failing if the job configuration being updated is already managed by another seed job.

This fix will resolve a scenario which has occurred more than a couple times at my company:

1. developer copies DSL from another team's repository w/ no changes
2. DSL is processed and developer realizes that they didn't update the DSL job definition(s) that were copied
3. developer then updates the copied DSL with new config/naming, deleting the original job(s) and all history

Running the original seed job for the repository that was copied from will restore the original job(s), but all history will be lost.

[jpederzolli]

@daspilker any chance of this getting merged or feedback? thanks!

[daspilker]

@jpederzolli Looks good so far. Can you change the wording from "job" to "item" as the check will also apply to folders. Job DSL is used in a variety of ways, so people may rely on the fact that a job can be generated by different seed jobs. Can you add a checkbox to the build step UI, so that users have to enable the check?

[jpederzolli]

Thanks @daspilker! Updates applied