Github Workflow that checks for CHANGELOG, breaking changes on PRs to published packages

It is easy to forget to add a `CHANGELOG` entry or introduce a breaking change to the packages in the DevTools repo that are published on pub (e.g. `devtools_shared`, `devtools_app_shared`).

We should add a Github workflow/s that can detect breaking changes and remind authors to add `CHANGELOG` entries, similar to the release notes check we currently have in place.

I think we could use https://github.com/dart-lang/ecosystem/tree/5c8a298e4042ebdc0819441036adac7ce4842c05/pkgs/firehose for the breaking changes check.

检查 DevTools 仓库中现有的 release-notes 检查，以及所引用的 dart-lang/ecosystem firehose 软件包。定义一个 GitHub workflow，检查 devtools_shared 和 devtools_app_shared 等已发布软件包是否存在 breaking changes，并提醒 pull request 添加 CHANGELOG 条目；当两个检查都针对相关 pull request 运行时，即视为完成。

由索引模型根据 Issue 内容生成。