Create a design of the page and get it approved

Created by: sashaostrikov

This is the first step of creating the UI for 1-click export page.

Link to proposed UI blueprint: https://sourcegraph.slack.com/archives/C02DUJRQP70/p1657502264142609?thread_ts=1656506211.384079&cid=C02DUJRQP70

/cc @jplahn @ryphil