CLI: Force welcome stories to show up first in load order

[shilman]

Issue: #7953

What I did

Rename the CLI templates:

• Welcome.stories.js => 0-Welcome.stories.js
• Button.stories.js => 1-Button.stories.js

This forces Welcome to the top and to show up first, without needlessly complicating the user's config with storySort or complicated configure logic.

How to test

Manually simulate the change in a fresh project:

npx create-react-app cra3
cd cra3/
npx -p @storybook/cli@next sb init
yarn storybook
cd src/stories/
mv Welcome.stories.js 0-Welcome.stories.js
mv Button.stories.js 1-Button.stories.js
cd ../..
yarn storybook

[vercel]

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[tmeasday]

Seems like the best way to do it for now :/