[docs] Add a migration guide with codemod for v5 -> v6

[joserodolfofreitas]

Summary

Following what we did from v4-v5, we need to create a migration page for v6 and feed it as we progress on the development.

This issue creates the initial page with the initial changes.

However, each PR introducing a breaking change in v6, should also:

1. In the PR’s description describe it. So we can then copy & paste the content into the changelog and the community understands what’s going on.
2. Update the migration guide with a new entry
3. Ideally add a codemod if possible, otherwise, skip it.

An example of what looks great: https://github.com/mui/material-ui/pull/26186.

Following there's a list of changes done before the migration guide

Date pickers PRs

Data Grid PRs