Maintenance: Split renderers preview entrypoints

[ndelangen]

What I did

When doing research how to optimize storybook compile time (sb build), @kasperpeulen discovered that we add docs related preview code even if addon docs isn't used.

This PR splits the injected code into 2 parts and ensures the docs related part is only injected when addon docs is active.

I renamed the config.ts (old naming scheme) file to entry-preview.ts and entry-docs.ts.
At first I had preview.ts and preview-docs.ts, but I found it hard to distinguish between entries by addons that were also called preview.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

• Create a sandbox using vite
• Remove addon docs.
  • remove .mdx extension for stories
  • remove addon-essentials (and optionally addon-docs too)
  • remove docs options (usually configured like: autodocs: 'tag')
  • remove any renderer (copied) specific stories
• add rollup-plugin-visualizer in main.ts:

   import { defineConfig } from 'vite';
   import react from '@vitejs/plugin-react';
  
   import { visualizer } from 'rollup-plugin-visualizer';
  
   export default defineConfig({
     plugins: [
       react(),
       visualizer({
         template: 'sunburst', // or sunburst
         open: true,
         gzipSize: true,
         brotliSize: true,
         filename: 'analyse.html', // will be saved in project's root
       }),
     ],
   });

• Inspect the opened webpage detailing the bundle stats.
• There should be no docs related code there. specifically the entry called "entry-docs" should NOT be there.

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>

[tmeasday]

I feel like I want the name "preview" in entry-docs somewhere. It's a "preview annotations file added for docs". Entry is ambiguous, as (a) you can have other entries, e.g. in the manager, and (b) it doesn't indicate the special preview annotations handling of exports.