Server side saved objects import / export API

[mikecote]

We will use this meta issue to track the proposed plan for server side import / export API. The main goals are to allow saved objects to automatically export their own dependencies and to allow import / export on any type of saved object.

Once complete, this should resolve the following issues:

• Saved object import/export - add extension point to retrieve saved object references for saved object type #26373
• Saved Objects import is successful although the associated index pattern is deleted.  #22559
• New objects API export without dependencies from the UI #22550
• Faster import of objects #23557
• Add Canvas workpads to Saved Object Management #23165
• Expose object import/export as an API #4759
• Saved object export/import API #16831
• [Kibana 6.4] Exporting objects with a search, shows exporting less objects, but exports all #22590
• "Could not locate index pattern id" after importing Kibana object (Data Control) #23892
• Consistent object sequence in Export Everything #29747
• Ability to export/import kibana advanced settings  #4265

Once complete, this should facilitate the following issues:

• Surface relationships between Saved Objects when saving #5947
• Ability to export/import kibana advanced settings  #4265

Phases

The completion of saved objects import / export API will be implemented in the following phases.

Phase 1 - Create saved object relationships

#27210

In this phase, we need to layout the groundwork for the enhancements we want to do to the import / export feature. In order to have automatic conflict discovery and automatic dependency exporting, we need to store at a generic level what each saved object has references to.

Phase 2 - Write a server side API for import / export

#4759

In this phase, we need to move existing functionality to the server side. We will also order the objects on export so the import API doesn't have to worry about the dependencies not being declared first. The import API will migrate the saved objects as needed.

Phase 3 - Use relationships to automatically export dependent data

#27306

In this phase, we will change the export API to automatically include nested dependencies.

Phase 4 - Support import / export for any type of saved object

#34862

In this phase more types of saved object will be supported for import / export and a few modifications to the saved object management UI will be made to handle UX for other types of saved object.

[elasticmachine]

Pinging @elastic/kibana-platform

[rayafratkina]

cc @mattkime