[Dashboards][Discuss] Returning saved object properties in responses from API

[nickpeihl]

There are several saved object metadata properties that we return in the API response. We should decide if/how we want to expose these properties. Because these properties are automatically updated by the saved objects client we only expose these in the response. These properties can not be created or modified by API consumers in requests. The only exception is id which can be optionally specified in the Create endpoint.

• id
• type
• updatedAt
• createdAt
• updatedBy
• createdBy
• managed

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)

[thomasneirynck]

See #158277.

The created/updatesBy properties, while useful in the API should not just bleed through without an explicit mapping.

[thomasneirynck]

Somewhat of a dupe of #197529. I'd merge these tickets under a single "clean up"