Upload files

{
  success: boolean,
  results: [{
    userId: string,
    ownerKey: string,
    location: string,
    locationPreview?: string,
    duration?: string,
    originalname: string,
    filename: string,
    mimetype: string,
    size: string,
    expiresAt: string,
    clientEncrypted: boolean,  // bytes are client-side ciphertext
    isPrivate: string,
    _id: string,
    createdAt: string,
    updatedAt: string,
  }],
}