code: public WikiAttachment uploadAttachment(Object projectIdOrPath, File fileToUpload, String branch) throws GitLabApiException {
  
          URL url;
          try {
              url = getApiClient().getApiUrl("projects", getProjectIdOrPath(projectIdOrPath), "wikis", "attachments");
          } catch (IOException ioe) {
              throw new GitLabApiException(ioe);
          }
  
          GitLabApiForm formData = new GitLabApiForm().withParam("branch", branch);
          Response response = upload(Response.Status.CREATED, "file", fileToUpload, null, formData, url);
          return (response.readEntity(WikiAttachment.class));
      }
docs: Uploads a file to the attachment folder inside the wiki’s repository. The attachment folder is the uploads folder.
  
  <pre><code>POST /projects/:id/wikis/attachments</code></pre>
  
  @param projectIdOrPath projectIdOrPath the project in the form of an Integer(ID), String(path), or Project instance, required
  @param fileToUpload the File instance of the file to upload, required
  @param branch the name of the branch, defaults to the wiki repository default branch, optional
  @return a FileUpload instance with information on the just uploaded file
  @throws GitLabApiException if any exception occurs