New post-signup flow + Stepper and Terminal components

Created by: artemruts

Description

This PR adds the post-sign-up (welcome) flow + a Stepper and Terminal components (@5h1rU )

Relevant links:

• New post-signup flow epic
• UX enhancements to new post-signup flow epic
• Design in Figma

Demo

https://user-images.githubusercontent.com/1319181/126425814-01ec3cf8-4bb9-4512-b994-7440709ef50f.mov

Notes 🚧

How to test in Dev (hard)

It could be hard to test the welcome flow in Dev because of:

• local repo caches
• feature flags
• local storage cache keys that prevent the user from going through the flow multiple times

Steps:

1. to enable the post sign up flow:

   a) (preferred way) enable enablePostSignupFlow experimental feature for the instance Experimental features can be found here: Settings -> Site Admin -> Site configuration -> experimentalFeatures

   b) add a user AllowUserViewPostSignup tag to your user Local DB access needed

2. to see private repositories: Set externalService.userMode to all in Site configuration (see above)

3. If you want repositories to be cloned again: remove rm -rf ~/.sourcegraph/repos/ directory (local cache)

4. to trigger the flow: sign out and register a new user

I tried adding some extra context in single comments to some files.

Todos

• Because of backend API limitation, we decided to change how the Terminal displays progress data. Now I need to confirm with @quinnkeast what UI/UX changes need to happen to make progress more easily readable.