CHANGELOG: Mention Kubernetes migration for 3.10
Created by: keegancsmith
CHANGELOG entry for https://github.com/sourcegraph/deploy-sourcegraph/pull/428
Part of https://github.com/sourcegraph/sourcegraph/issues/5725
Created by: keegancsmith
CHANGELOG entry for https://github.com/sourcegraph/deploy-sourcegraph/pull/428
Part of https://github.com/sourcegraph/sourcegraph/issues/5725