insights: [frontend] don't re-calculate data series that are already calculated by the API

Created by: coury-clark

Discovered as part of https://github.com/sourcegraph/sourcegraph/issues/27435

If the API / backend pre-calculates a series that is not global (non-null / non-empty) the frontend (webapp) will attempt to recalculate the series just in time. This poses a problem for capture groups series that are calculated by the backend.