feat: start / stop exception autocapture programatically

[daibhin]

Problem

We're trying to give people more control over when error tracking exception autocapture is enabled

Changes

Expose a method that allows them to enable and disable exception autocapture via the posthog client

Libraries affected

• [ ] All of them
• [x] posthog-js (web)
• [ ] posthog-js-lite (web lite)
• [ ] posthog-node
• [ ] posthog-react-native
• [ ] @posthog/react
• [ ] @posthog/ai
• [ ] @posthog/nextjs-config
• [ ] @posthog/nuxt
• [ ] @posthog/rollup-plugin
• [ ] @posthog/webpack-plugin