[WIP] Example todo union type embeddable

[ThomThomson]

Summary

This is a quick & dirty example of using a union type and type guards to allow an embeddable to work seamlessly with either value or reference types without sacrificing typing.

#62698 is a similar (better) example of an embeddable that works with either reference of value, but it uses optional parameters for attributes and the savedObjectId. This PR instead uses a union type e.g. export type TodoComboInput = TodoComboValInput | TodoComboRefInput; to ensure that the input is either by value or by reference, with nothing in between.

Pros of this approach

1. There is only one embeddable to maintain
   2: Embeddables can define their own loading states
   3: Helps to decouple embeddables from savedObjects

Adding a new embeddable of type "Todo (by reference or value)" using the add panel option in the dynamically adding children example will randomly create an instance of the embeddable by value or by reference.

For maintainers

• This was checked for breaking API changes and was labeled appropriately

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: c5227d4

History

• 💔 Build #42314 failed dc8f19c

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[ThomThomson]

Closing in favor of #68719