Enabling the code insights feature flag isn't enough to see others' code insights (because you still have to enable the extensions)

Created by: Joelkw

Issue: if a user wants to see their teammates' org or globally visible insights but doesn't have code insights available, then they add the flag to their settings and expect to now see code insights. Although the flag in their settings does now enable them to see the "insights" item in their navbar and see the dashboard pages, it doesn't "turn on" the search-insights (or code-stats-insights" or other) Sourcegraph extensions.

This means that the user still sees blank dashboards until they go to the registry, turn on the extensions, and re-view the insights pages. Previously we didn't hit this bug because we "automatically" turn on extensions when you create insights – but if the user doesn't want to create insights, just view others', it's a problem.

I will temporarily fix this in docs – but we should make sure we fix this somehow when we remove the "experimental" feature flag for insights (ie, turn it on by default) in 3.32.