Batch exports: Support for PostHog annotations model

[tomasfarias]

Feature request

Describe the solution you'd like

Batch exports supports exporting models like the persons and events model. However, there is no support for batch exporting PostHog annotations. As a user, I would like to batch export this data to get access to make associations with other batch exported data, like events. As afar as I can imagine, the model can be relatively simple, mostly mimicking the object returned by our API: https://posthog.com/docs/api/annotations#get-api-projects-project_id-annotations

Describe alternatives you've considered

Querying the API directly is an option, but batch exports is a more complete package.