Help: Use ExternalLink component in search results

[dllh]

Repro:

1. Go to /help
2. Perform a search.
3. Observe the results.

They'll look something like this:

The results right now link to documents not inside Calypso. Elsewhere it had been suggested that we use <ExternalLink> for external links. It shows the little arrow indicating that the link will go off-site (see e.g. #1229). I imagine we probably need to do the same for these search results.

[stale]

This issue has been marked as stale because it hasn't been updated in a while. It will be closed in a week. If you would like it to remain open, can you please comment below and see what you can do to get things moving with this issue? Thanks! 🙏