Allow Datasource Schema JSON Export

Feature request

Is your feature request related to a problem?

Problem: It is currently too difficult to get an LLM to generate posthog insight queries. As a user I want to be able to speak freely with any LLM about my data, with them having as much context as possible on the data.

Max is cool but not as capable as some other LLMs on codegen.

Describe the solution you'd like

I propose

Level 1:
Schema Export - Export the data of all your available tables

Level 2:
LLM Context Export - Export all of you schema as well as a single row per table so an LLM can gain insight into type information. Potentially make the data slice have some configuration options.

Describe alternatives you've considered

At the moment I've had to painstakingly describe my schema to the LLM, or manually make files which deliver enough context to generate the queries I'm after.

Additional context

Thank you!

Debug info

- [ ] PostHog Cloud, Debug information: [please copy/paste from https://us.posthog.com/settings/project-details#variables]
- [ ] PostHog Hobby self-hosted with `docker compose`, version/commit: [please provide]
- [ ] PostHog self-hosted with Kubernetes (deprecated, see [`Sunsetting Kubernetes support`](https://posthog.com/blog/sunsetting-helm-support-posthog)), version/commit: [please provide]

No files, tests, or entry points are named. First clarify whether Level 1 schema export or Level 2 LLM context export is in scope, then identify the datasource and table metadata entry points; done should mean an export containing the available table schemas, with sample rows and configuration only if Level 2 is accepted.