code: public GitlabBuildVariable createBuildVariable(Integer projectId, GitlabBuildVariable variable)
              throws IOException {
          String key = variable.getKey();
          String value = variable.getValue();
          return createBuildVariable(projectId, key, value);
      }
docs: Creates a new variable.
  
  @param projectId The ID of the project containing the variable.
  @param variable  The variable to create.
  @return The newly created variable.