release: add deploy-sourcegraph-docker docs updates to release tool

Created by: bobheadxi

The sourcegraph/server and deploy-sourcegraph equivalents of the changes done in https://github.com/sourcegraph/deploy-sourcegraph-docker/blob/master/RELEASING.md#update-documentation--publish-notifications is done by the release tooling currently, we should remove this manual step and automate it in the same PR.