Improve usefulness of changelog by listing changes in dependencies

Hi! Whenever we update our packages I like to try and provide a compact changelog in the commit description, but I've noticed that this is pretty difficult with the current changelog format for this monorepo.

Often changes are deeply nested, meaning you have to click through the changelogs of multiple packages until you find what actually changed (and then remember which package updates only contained dependency updates so you can skip them).

For an extreme example, consider the recent release of `postcss-preset-env` version `10.0.0`. The [changelog](https://github.com/csstools/postcss-plugins/blob/main/plugin-packs/postcss-preset-env/CHANGELOG.md#1000) in this repo is a huge list of major version bumps of various dependencies, which themselves each have a dependency tree, but I think the actual list of changes is something like this:

* Support for Node v18+
* [css-color-parser] fix `serializeP3` when `gamutMapping` is `false`
* [css-tokenizer] Improve performance
* [postcss-nesting] Make edition `2024-02` the default
* [postcss-content-alt-text] Add specific handling of `content: ">" / "";` as this pattern is used in the same way as ``, i.e. to represent an item that does not need a text alternative.

It would be great if changes to dependencies could be added at the top of the changelog in a format similar to the above, with identical changes being merged ("Support for Node v18+" would be harder to deduplicate, but it's an exceptional case).