code: public GitlabBuildVariable createBuildVariable(
              Integer projectId,
              String key,
              String value) throws IOException {
          String tailUrl = GitlabProject.URL + "/" + projectId + GitlabBuildVariable.URL;
          return dispatch().with("key", key)
                  .with("value", value)
                  .to(tailUrl, GitlabBuildVariable.class);
      }
docs: Creates a new build variable.
  
  @param projectId The ID of the project containing the new variable.
  @param key       The key of the variable.
  @param value     The value of the variable
  @return The newly created variable.
  @throws IOException on gitlab api call error