#4050 insights layouts & misc improvements

[paolodamico]

Changes

This PR continues our saga to improve the query experience from #4050; particularly builds up on #4296.

• Implements custom layouts for retention, sessions & paths (based on [Product & Design] - Revamp insights experience #4050 (comment)).
• Hides the formula input by default behind an "Add formula" button to follow convention of global filters and breakdown. Further, the button is disabled if the trend graph has only one series (with a prompt to add another series to be able to use formulas).

• Removes global filters from lifecycle graph. As only one series can be used, filters can be applied locally.
• Adjusts UI & location of remove button for each graph series.
• Miscellaneous UX improvements across insights.

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

[samwinslow]

LGTM!! Really tiny bits of feedback, mostly copy suggestions. 🚢

[samwinslow]

This is outside the scope of this PR but do you think it would be useful to have filters on retention? E.g. if I want to track retention of users on two Pageview events, one on Sign-In Page and the other on Activity Business Value Stuff Page.

[paolodamico]

Thanks for the quick review here @samwinslow! Re retention filters, if I remember correctly, there was a backend limitation for this that required use of actions? I believe it was due to computations on-the-fly timing out in PostHog. CC @EDsCODE

[paolodamico]

Merging as failing checks are unrelated.