Add sx prop to top level components

[bryanjtc]

Allow styling components like MultiFileUploadProps and SingleFileUploadProps by using the sx prop to customise the FileDropzone and the FileUpload

[NicholasMata]

With the latest version v1.0.0-alpha.4 sx is now available on the top level components

MultiFileUpload

<MultiFileUpload
  sx={{
    dragZoneSx: (state) => { border: state.dragActive ? 'green' : 'blue'}
  }}
  ...
/>

SingleFileUpload

<SingleFileUpload
  sx={{
    dragZoneSx: (state) => { border: state.dragActive ? 'green' : 'blue'}
  }}
  ...
/>