Add 'webkitRelativePath' support for uploads using <input>

[Nikita-schetko]

Hey guys! Maybe we can add support of 'webkitRelativePath' here ? It would be really helpful, because will give consistent behaviour for dragNdrop and just browser folder selection (using 'directory' mode)

    <input 
      type="file" 
      #fileSelector 
      [accept]="accept" 
      [attr.directory]="directory || undefined" 
      [attr.webkitdirectory]="directory || undefined"
      [attr.mozdirectory]="directory || undefined"
      [attr.msdirectory]="directory || undefined"
      [attr.odirectory]="directory || undefined"
      [multiple]="multiple"
      (change)="uploadFiles($event)" 
      class="ngx-file-drop__file-input" 
    />