Splits the insights page into separate sections with their own separate
filters. Each filter is sticky to the top of the page, similar to how
the previous filters worked.
In doing this, I have also moved around a lot of code. Refer to the
inline comments for more specific examples, but on a high level, this
PR:
- Moves the flag check from InsightsCharts into Insights itself. Because
the old Insights had filters and state, and the new one does not, it
made sense to fork off higher up in the tree. Because the new version
doesn't have state, I have also simplified it and removed an
intermediate component (InsightsCharts) that doesn't feel necessary
anymore.
- Because InsightsCharts isn't used anymore, I've moved the
LegacyInsightsCharts file back into InsightsCharts. However, I'm happy
to move it back if we think that's useful.
- Instead of all charts living in InsightsCharts, I've split each
section into its own file in the new sections directory. Because the
sections have separate filters, they don't share any state anymore, so
there's nothing they share.
- I'm reusing the existing hook and endpoint. As it stands, the
performance insights use **most** of the data from that payload (but not
all of it). The user insights use some of it. Flag lifecycle insights
doesn't use anything, but I've wired it up to make the filters work. I
expect that we'll iterate on the API endpoints etc later.

We're migrating to ESM, which will allow us to import the latest
versions of our dependencies.
Co-Authored-By: Christopher Kolstad <chriswk@getunleash.io>