insights: prototype search match count trend insights on search screen

[Joelkw]

Like a trend metric that click-expands to a graph, or a full graph on the side panel of the search screen. Okay if it doesn't work for all-repo searches first.

Roadmap issue: https://github.com/sourcegraph/sourcegraph/issues/38440

[sourcegraph-bot-2]

Heads up @Joelkw @felixfbecker @vovakulikov @unclejustin - the "team/code-insights" label was applied to this issue.

[Joelkw]

Notes from sync – backend work might be very light here if similar to the hackathon.

Frontend – big problem, is that we need to put enterprise-like UI in the search UI, and this will be difficult to do properly. We can do it in a hacky unstable way, but if we need a proper solution, probably possible.

[vovakulikov]

@Joelkw @AlicjaSuska a few quiestions

• What is the reason to have two issues for this prototype (this issue and roadmap issue)? Can we use just roadmap issue as an entry point for it, or roadmap issue should be used only in product and eng product board?

• I suspect that this is an experiment we want to flag this feature with feature flag, do we want to put this behind the "simple UI mode" experimental feature flag?

• In designs I see that this prototype implies that it will be placed in the side panel but we have this panel only in "Simple UI mode". Does this mean that code insight live preview will be available only in this mode?