Make collectionPopulationRequestHandler available in @payloadcms/live-preview

[janus-reith]

mergeData allows to set a custom function for the fetch request handler:
https://github.com/payloadcms/payload/blob/main/packages/live-preview/src/mergeData.ts#L76

const requestHandler = args.collectionPopulationRequestHandler || defaultRequestHandler;

But that arg isn't passed over to mergeData in handleMessage:
https://github.com/payloadcms/payload/blob/main/packages/live-preview/src/handleMessage.ts#L46

Currently it is not possible to pass down a custom function when using the @payloadcms/live-preview package.
It would be nice if that parameter could be passed down to mergeData:

const { subscribe, unsubscribe, ready } = await import(
  "@payloadcms/live-preview"
);

subscription = subscribe({
  callback: onChange,
  depth,
  initialData,
  serverURL,
  collectionPopulationRequestHandler: ({ apiPath, endpoint, serverURL }) => {
    // Something custom here
  },
});

[janus-reith]

Opened a PR: #10947