npm package: Store posthog as a global variable

[MarconLP]

Is your feature request related to a problem?

When trying to debug client websites that are not using the snippet, I am unable to access posthog through the console. Which is making debugging hard.

Describe the solution you'd like

A way to access posthog through the config. Solutions:

1. When a window var like POSTHOG_DEBUG is set, we could log out posthog as a variable.
2. A button in the toolbar that will log out posthog as a variable.
3. log out posthog as a variable when toolbar is being loaded.

Additional context

https://posthog.slack.com/archives/C04MZFDA5KK/p1699535586640289

Thank you for your feature request – we love each and every one!

[pauldambra]

there's now at least one way to do this PostHog/posthog-js#1108