Add "include" option for shell jobs

Current Situation

• Shell jobs in JS1 provide an <include> element that can be used to provision scripts to an Agent. Typically such scripts represent function libraries that are used by the job script.
• Similar features are provided by competitor products.

Desired Behavior

• A new "versioned item" is available for shell code (more generally: any sort of code) that is deployed to a Controller and Agents that are used for execution of the workflow/job.
• A job can reference a number of such "included" items similar to the JS1 <include> element.
• When executing the job then the contents of the "included" item is prepended the job script.

Maintainer Notes

• The requested feature is available from JOC-1170