Storybook: [Angular] Add moduleMetadata once

[scottkipfer]

Issue details

Feature Request: It can get tedious adding the same moduleMetadata for every story. Could it be possible to add it once at the parent level? I added a code snippet bellow to help clarify my request.

Screenshots / Screencast / Code Snippets (Optional)

Current: AppMoudle must be provided for each story.

import { storiesOf } from '@storybook/angular';
import {AppModule} from "../src/app/app.module";

import {ButtonComponent} from "../src/app/button/button.component";

storiesOf('Buttons', module).add('Button', () => ({
  component: ButtonComponent,
  props: {
    buttonText: 'Button',
    buttonColor: 'primary'
  },
  moduleMetadata: {
    imports: [AppModule]
  }
})).add('Button With Icon',() => ({
  component: ButtonComponent,
  props: {
    buttonText: 'Button',
    buttonIcon: 'account_circle',
    buttonColor: 'warn'
  },
  moduleMetadata: {
    imports: [AppModule]
  }
})).add('Disabled Button', () => ({
  component: ButtonComponent,
  props: {
    buttonText: 'Disabled',
    disabled: true
  },
  moduleMetadata: {
    imports: [AppModule]
  }
}));

Example: AppMoudle is imported before any stories are added.
```
import { storiesOf } from '@storybook/angular';
import {AppModule} from "../src/app/app.module";

import {ButtonComponent} from "../src/app/button/button.component";

storiesOf('Buttons', module).imports([AppModule]).add('Button', () => ({
component: ButtonComponent,
props: {
buttonText: 'Button',
buttonColor: 'primary'
}
})).add('Button With Icon',() => ({
component: ButtonComponent,
props: {
buttonText: 'Button',
buttonIcon: 'account_circle',
buttonColor: 'warn'
}
})).add('Disabled Button', () => ({
component: ButtonComponent,
props: {
buttonText: 'Disabled',
disabled: true
}
}));```

[amcdnl]

I agree with the use case but I think something like:

storiesOf('Buttons', module)
   .addDecorator(moduleMetadata({ inputs: [MyModule] }))
   .add(...)

would be more in line with the API.

[jonrimmer]

We had the same requirement. I created this decorator, which can be used as @amcdnl suggested:

import { NgModuleMetadata } from '@storybook/angular/dist/client/preview/angular/types';

export const moduleMetadata = (metadata: Partial<NgModuleMetadata>) =>
  (context: () => any) => ({
    moduleMetadata: metadata,
    ...context()
  });

Individual stories should be able to override the default metadata with their own. A more robust implementation could try to merge the two.

[amcdnl]

@jonrimmer - Very nice! You should PR this.

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