Created by: sashaostrikov
This is the first PR of 1-click export effort. This includes ExportRequest processing, site config fetching and redacting and creating a zip archive.
️ This PR targets the branch of this PR
Closes https://github.com/sourcegraph/sourcegraph/issues/39616 and https://github.com/sourcegraph/sourcegraph/issues/39619
New test is added.
Push commits to the source branch or add previously merged commits to review them.
