[D&D] Research on how plugins create and store reference objects

[abbyhu2000]

Requirements:

• Research on how other plugins are creating reference object and how are they being stored
• What are the relationships among KibanaSavedObject, search source and reference object
• For [D&D] Ensure relationships to index patterns are saved correctly #1878, explore the option to skip the steps and create reference object directly
• Document findings here

[joshuarrrr]

Great list! While we can start by documenting the findings here, we'll also want to make sure they're saved somewhere under version control (as a README or other tutorial) so they're discoverable.