[Doc] Add details about Datagrid to DataTable migration

[Madeorsk]

Problem

We have a codemod, but it doesn't do everything. Besides, how to check that it did the right job?

Solution

• List all the things the codemod does (e.g. replace Datagrid by DataTable)
• List all the things it doesn’t do and that must be done by hand (e.g. remove DatagridConfigurable)

Additional Checks

• The PR targets master for a bugfix or a documentation fix, or next for a feature
• The documentation is up to date