Create a VSCE specific Watch & Learn video for VSCE default search page

Created by: jjinnii

Users unfamiliar Sourcegraph will be trying code search for the first time through the VSCE. While the current Search Watch & Learn video is great, it would be much more powerful to have a video specific to the extension. There is a need to explain what it means to open a file in VS Code through Sourcegraph's extension (is it editable?), as well as explain why a sourcegraph account is needed to enable search on private code. (does private code all my repos local or just repos synced to Cloud?) We've even received these questions internally from marketing/community team, so we know users will have the same questions when first using the extension.