Issue: #20552
## What I did
I added a new builder option for the Vite builder named `viteConfigPath`, which is a path to a custom config relative to the cwd. If the path does not resolve, a clear error will be thrown with the absolute path being checked.
I also added a new utility, `getBuilderOptions()`, which is helpful because these options can be specified two different ways, with `core.builder.options` or `framework.options.builder`. The utility gives an easy way to check both. It gives preference to ~`core.builder.options`~ `framework.options.builder`, since that's the newer way to define the options.
## How to test
1. `yarn task --task sandbox --start-from auto --template react-vite/default-ts`
2. Move the `vite.config.ts` file into `.storybook`
3. Add an alias, like:
```ts
export default defineConfig({
plugins: [react()],
resolve: {
alias: {
stories: path.resolve(__dirname, '../src/stories'),
},
},
});
```
4. Change one of the stories to use this alias, such as the Button story:
```ts
import { Button } from 'stories/Button';
```
5. Start Storybook, it will fail
6. Add `viteConfigPath: ".storybook/vite.config.ts"` to the builder options in `.storybook/main.ts`
7. Restart storybook, and it should work.
## Checklist
<!-- Please check (put an "x" inside the "[ ]") the applicable items below to make sure your PR is ready to be reviewed. -->
- [ ] Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
- [X] Make sure to add/update documentation regarding your changes
- [ ] If you are deprecating/removing a feature, make sure to update
[MIGRATION.MD](https://github.com/storybookjs/storybook/blob/next/MIGRATION.md)
Is there a way to create an automated test for this? I couldn't think of a good way to do it.
#### Maintainers
- [ ] If this PR should be tested against many or all sandboxes,
make sure to add the `ci:merged` or `ci:daily` GH label to it.
- [X] Make sure this PR contains **one** of the labels below.
`["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]`
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