Allow async transform docs.source.transform

[SimmeNilsson]

Is your feature request related to a problem? Please describe.

Prettier has recently switch to an async API.
We are using prettier format in docs.source.transform.
https://storybook.js.org/docs/html/api/doc-block-source#transform

Describe the solution you'd like

Would it be possible to allow for a Promise to be returned from transform?

Describe alternatives you've considered

Tried @prettier/sync but it is dependent on node worker_threads. Breaks storybook build.

Are you able to assist to bring the feature to reality?

no

Additional context

Example of usage, but format is async in prettier 3.x.
transform: (input: string) => { return prettier.format(input, { parser: "html", plugins: [prettierHtml] }); }

[omarkawach]

Also interested in this

[vprothais]

The HTML preview addon needs Prettier 3 to format source in Story view, but we can't use Prettier 3 if we use prettier in docs.source.transform.

[valentinpalkovic]

Fixed by #30426