Plugin editor types

[mariusandra]

Changes

• Adds @posthog/plugin-scaffold types into the plugin source editor for sweet TypeScript support
• Changes the default plugin to one that encourages discovery (loosely based on @Twixes 's advanced plugin kit)
• This is just the first step though. We should add types for all other exported packages (e.g. aws sdk, plugin contrib, ...) as well.

Checklist

• All querysets/queries filter by Organization, by Team, and by User
• Django backend tests
• Jest frontend tests
• Cypress end-to-end tests
• Migrations are safe to run at scale (e.g. PostHog Cloud) – present proof if not obvious

[Twixes]

There is a problem in that this doesn't build

[Twixes]

This should match defaultConfig.

[mariusandra]

So, feedback addressed and it builds now. Still some issues with this PR. Not sure if they are blockers or not:

• We only have types for anything imported from @posthog/plugin-scaffold. No types for fetch or any of the other packages like aws-sdk here.
• As an improvement, I'd suggest adding two things to plugin-scaffold: 1) all pinned versions of all packages that plugin authors can import from into devDependencies, a build script that copies the types of all those packages into the plugin scaffold package for exporting. The posthog would just take these types from inside scaffold, instead of requiring us to install aws-sdk and other large things that slow down builds.
• We need to make sure to keep posthog, plugin-server and plugin-scaffold versions in sync. Automatic github actions could help.

[Twixes]

Nice.
As for improvements, I'd say nothing blocking. May be worth creating issue for some e.g. ensuring plugin-scaffold is up to date.