Create a storybook for self-serve Cody pages

[vdavid]

Context:

• We have pages in Storybook for alerts and other atomic components. Example: alerts
• We also have pages for more complex components. Example: web/batches.

Problem:

• Currently, folks have to have the whole dev environment running whan making small changes to the design, which is often inconvenient. Example: https://github.com/sourcegraph/sourcegraph/pull/63356 – Rob had to have the entire stack set up and the DB in a state where he could see the banners.

Solution:

• Map out what pages we have, which ones are the main components, what states they have, and create the Storybook pages from them.

We currently have these pages:

• Dashboard: /cody/manage
• Subscription: /cody/subscription
• Checkout (individual): /cody/manage/subscription/new
• Checkout (team): /cody/manage/subscription/new?seats=5
• (ADMIN) Manage subscription: /cody/subscription/manage
• (ADMIN) Manage team: /cody/team/manage
• (ADMIN) Add seats: /cody/manage/subscription/new?addSeats=1