Get ready to switch to this repo as source for our builds

[pauldambra]

• support alternate recorder scripts in posthog-js
• support alternate recorder script in remote config/decide
• be able to version the packages we need here
• be able to publish the packages here
• copy over all PRs / recreate from patches to keep prod behaviour
• publish packages on appropriate signal (e.g. merge to main
• setup posthog-js to use this or upstream rrweb