Use trends legend graph everywhere

[alexkim205]

Changes

Fixes #4484.

This replaces today's non-informative Insight tables with a table display we already have for our line graphs (less the checkbox legend key)

Changes in this CR

• Refactored rendering Insight graphs logic
• Generalized <TrendLegend/> into <InsightsTable/>
• Changed to using this new table view in Trends, Sessions, and Stickiness
• Conditionally added total count column to table.
• More typing

P.S. - I didn't change the existing table view for Insights>Sessions>Distributed Session Lengths, because the data looks a bit different than what is required for <TrendTable/> and would need super specific data munging. For this reason, I fallback to <ActionsTable/> as shown here. Let's deprecate this later (or at least refactor. It seems overdue for some cleanup)

Before

After (for Trends, Sessions, and Stickiness tabs)

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
• Frontend/CSS is usable at 320px (iPhone SE) and decent at 360px (most phones)

[paolodamico]

🚢 great stuff! made some minor changes to follow naming conventions and decided to feature flag the total column because we need to handle the special case of unique users, because the plain sum could cause confusion (as it would likely lead to duplicate users because it's not unique across the entire period). Let's discuss this in a separate PR.