web: Fork cloud sign-up page for VS Code users

Created by: philipp-spiess

Fixes https://github.com/sourcegraph/sourcegraph/issues/29703

🚨 This is a preview PR until we have a final copy

The idea here is that for users coming via the VS Code extension, we likely want a custom copy.

Right now, we are already a couple of different versions of the sign-up flow:

• A regular cloud signup flow
• A regular on-prem signup flow (which does not contain marketing copy)
• A signup-optimized flow that is currently being tested. We can disregard this as it's going away soon
• An ?invitedBy=username that is being worked on by @slimsag

For the VS Code sign-up copy I decided to make a cleaned up fork of the regular cloud signup flow. I decided to remove the invited by logic because when users get an invite link, it should take precedence over their VS Code referrer. I also ignored the on-prem signup since it currently does not have any marketing text so an adjustment for VS Code won't make sense.

The new page can be opted into by including vs-code in the query search params, e.g.:

https://sourcegraph.test:3443/sign-up?vs-code=1&showEmail=true

Outstanding Issues

• I need access to the Figma account so that I can extract the proper VS Code icon.
• The subtitle breaks to two lines with the font that we use on the signup page. Should we change something there?