[Files] Add meta prop to <FilePicker /> (#151417)

## Summary

Added the `meta` prop to the `FilePicker` component, also pass this down
to the `FileUpload` component so that files created via the picker can
have meta set.

Close https://github.com/elastic/kibana/issues/151375

## How to test

1. Start Kibana with examples `yarn start --run-examples`
2. Go to the "Developer examples" in the side-nav menu under analytics
3. Go to "Files example"
4. Upload a file via the "Select file" button, should present an empty
file picker if you have no files, otherwise use the little upload
component bottom left
5. Either select files or dismiss the modal
6. Inspect the uploaded file and see the `myCool: 'meta'` entry included
with other metadata

## Screenshot

A file uploaded via the `FilePicker` in the "Files example" plugin.

<img width="897" alt="Screenshot 2023-02-16 at 11 41 06"
src="https://user-images.githubusercontent.com/8155004/219342872-c39b5d81-7421-4187-bb1c-d6815d80a3dc.png">


### Checklist

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

examples/files_example/public/components/app.tsx

@@ -174,6 +174,7 @@ export const FilesExampleApp = ({ files, notifications }: FilesExampleAppDeps) =
             notifications.toasts.addSuccess({
               title: 'Uploaded files',
             });
+            refetch();
           }}
           onDone={(ids) => {
             notifications.toasts.addSuccess({

examples/files_example/public/components/file_picker.tsx

@@ -27,6 +27,7 @@ export const MyFilePicker: FunctionComponent<Props> = ({ onClose, onDone, onUplo
       onDone={(files) => onDone(files.map((f) => f.id))}
       onUpload={(n) => onUpload(n.map(({ id }) => id))}
       pageSize={50}
+      uploadMeta={{ myCool: 'meta' }}
       multiple
     />
   );