Document entity configuration

[oandregal]

The core-data package is at the center of Gutenberg's data pipeline, and it pivots on declaring some configuration for the entities it works with.

This issue tracks the properties and behaviors we need to document:

• baseURL: Initial documentation of entity configuration #55103
• baseURLParams: Initial documentation of entity configuration #55103
• getSyncObjectId: part of the sync experiment. Probably not to document at the moment.
• getTitle:
• key: Initial documentation of entity configuration #55103
• kind: Document kind, name, plural for entity config #55158
• label:
• name: Document kind, name, plural for entity config #55158
• plural: Document kind, name, plural for entity config #55158
• rawAttributes:
• syncConfig: part of the sync experiment. Probably not to document at the moment.
• syncObjectType: part of the sync experiment. Probably not to document at the moment.
• transientEdits: