[Feature request] Add support for versioned documentation

Flutter releases a major version every three months, and the corresponding documentation is updated accordingly; however, once the documentation is updated, it is no longer possible to view the documentation for previous versions.

I would like to request the addition of support for accessing documentation for older versions.

[Versioning](https://docusaurus.io/docs/versioning)

[Docs Multi-instance](https://docusaurus.io/docs/docs-multi-instance)