Code Insights: Use author date instead of commiter date

Created by: vovakulikov

Background

For some reason, our BE started returning bad dates for some queries of some repos.

For code search insight we build a query with before: DATE_A filter but it turned out that our API returned commit with DATE_B which is greater than DATE_A (so before the filter has been violated

So we throw an error about this here https://sourcegraph.com/github.com/sourcegraph/sourcegraph/-/blob/client/web/src/enterprise/insights/core/backend/api/get-search-insight-content/get-search-insight-content.ts?L214:52

Incident slack channel https://sourcegraph.slack.com/archives/C02H7MVAPK9 We still don't know what is the reason and why now this problem appeared but it seems like using author-date instead of commuter date fixes this problem. (but maybe it's just corner case and the problem is still there)