insights: design for in-line or in-flow references to insights

[Joelkw]

For this item #38441 , we need designs for:

1. When the insight references a line/section
2. When the insight references a file (select:file)
3. When the insight references a repo (select:repo)
4. Stretch/bonus – when the insight references a smaller scope (e.g., a line or file) but we display it on the larger scope (e.g., file or repo) – like showing somehow an insight is referenced in the file tree, or the repo, even if the reference is just to a line.

[sourcegraph-bot-2]

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