How to use the just-scripts-utils.readRushJson function in just-scripts-utils

return async function upgradeRepo() {
    const rootPath = findMonoRepoRootPath();

    if (!rootPath) {
      logger.error('Could not find monorepo root path. Not upgrading anything.');
      return;
    }

    const resolveStacks = getResolvedStackVersions(path.join(rootPath, 'scripts'));
    const stackDiffs = await getStackDiffs(rootPath, resolveStacks);

    if (stackDiffs) {
      let didUpgradeProjects = false;

      // For each package, look for stacks that match, and apply upgrade for the project
      const rushConfig = readRushJson(rootPath);
      if (!rushConfig) {
        logger.error(`Could not read rush.json under ${rootPath}. Not upgrading anything.`);
        return;
      }

      await rushConfig.projects.reduce(async (currentPromise, project) => {
        await currentPromise;

        if (project.projectFolder !== 'scripts') {
          const projPackageJson = readPackageJson(path.join(rootPath, project.projectFolder));

          if (projPackageJson && projPackageJson.just && projPackageJson.just.stack) {
            const diffInfo = stackDiffs[projPackageJson.just.stack];

            // no diff info means that there isn't any diffs to apply
            if (diffInfo) {