Instrument toolbar

[paolodamico]

Changes

Introduces basic instrumentation to the toolbar.

• Introduces the toolbar mode triggered event which is fired when any of the toolbar modes (heatmap, inspect, stats, ...) are activated/deactivated.
• Introduces the toolbar selected HTML element event which is fired when an element in the host's website is clicked for further details.
• Adds UTM tags to the help url for the toolbar button so we can track on the docs when this button is clicked.
• Introduces the toolbar dragged event which is fired after the toolbar has been dragged and is dropped somewhere in the screen.
• Introduces the toolbar loaded event which is fired when the toolbar component is loaded.

Checklist

• All querysets/queries filter by Organization, by Team, and by User
• Django backend tests
• Jest frontend tests
• Cypress end-to-end tests

[paolodamico]

@mariusandra when you get a chance to review this would you mind making sure all the events are properly triggered? Want to make sure we don't have weird events coming in that affect our metrics. I also ran into an issue sending events with posthog.capture at some point, but I think that was my computer.

[mariusandra]

The big issue with this PR is that you're using posthog-js, which won't work here. Instead you should import { posthog } from '~/toolbar/posthog' and capture via that.

I'm not sure if posthog-js would work now or not, but the original issue (and the reason for writing posthog-js-lite in the first place) was that I could not easily include two copies of posthog-js on a page at the same time. The toolbar is always running on a site that already has a copy of posthog-js running and sending events for the client. We need to be careful not to send the "toolbar button clicked" events to the client, but to ourselves.

I'll see what can be done regarding the other questions...

[mariusandra]

I updated the posthog library to the right one, fixed some type errors and added information about the action and heatmap counts. It's probably OK to merge now, but please test :)

[paolodamico]

Thanks for the review and suggestions, made some additional changes. Looks good to merge to me, but feel free to review once more before merging (will merge tomorrow otherwise). Also worth noting, noticed that we don't self-capture toolbar events in development, but keeping that for a separate PR.

[mariusandra]

Looks good!