Missing flutter version for MacOS dev setup docs

The [issue](https://github.com/AppFlowy-IO/AppFlowy/issues/3154) is from the main AppFlowy repo.

> ### Bug Description
>
> While I was building from source I faced an issue with the Flutter version.
> ### How to Reproduce
>
> While trying to build from source in MacOS using the [link](https://docs.appflowy.io/docs/essential-documentation/contribute-to-appflowy/software-contributions/environment-setup/building-on-macos)
> ### Expected Behavior
>
> A requirement at the top of the build instructions should be available showing the currently supported version of flutter, rust, and other dependencies for a successful build.
> ### Operating System
>
> MacOS
> ### AppFlowy Version(s)
>
> 0.2.8
> ### Screenshots
>
> ### Additional Context
>
> _No response_

While the flutter version is not specified in the [docs](https://docs.appflowy.io/docs/documentation/appflowy/from-source/environment-setup/building-on-macos). The script scripts/install_dev_env/install_macos.sh automates the fetching of the flutter version and specifies which version to use.

The flutter version is specifically mentioned in both the [linux](https://docs.appflowy.io/docs/documentation/appflowy/from-source/environment-setup/building-on-linux#install-flutter-three-different-methods) and [windows](https://docs.appflowy.io/docs/documentation/appflowy/from-source/environment-setup/building-on-windows#step-2-install-your-build-environment) doc.