Consider inserting fillers between lines in manifest files

We have a large monorepo that uses manifests. The manifest file is of course a JSON file that includes a line for each package, that is updated whenever a new version of the package is released. We frequently release multiple packages in succession (in separate PRs). If two of those packages are adjacent in the manifest file, this causes git conflicts since the PRs independently try to modify adjacent lines in the same file.

Our current workaround has been to insert filler lines in our [manifest file](https://github.com/googleapis/google-cloud-ruby/blob/main/.release-please-manifest.json), in the form of a "fake" package following each real package, to separate out the real packages and ensure that no two occupy adjacent lines in the file. This seems to be working for us for now, but maybe we can consider building a solution into the tool itself.