[docs] Add migration to DataGrid v6 page

[m4theushw]

Part of #5698

Preview: https://deploy-preview-6235--material-ui-x.netlify.app/x/react-data-grid/migration-v5/

[mui-bot]

These are the results for the performance tests:

Test case	Unit	Min	Max	Median	Mean	σ
Filter 100k rows	ms	603.3	1,055.8	675.7	815.46	168.639
Sort 100k rows	ms	666.5	1,302.8	1,302.8	1,013.96	224.619
Select 100k rows	ms	219.4	295.5	255.7	252.72	29.383
Deselect 100k rows	ms	144.5	252.5	209.3	204.26	34.663

Generated by 🚫 dangerJS against ff9c287

[joserodolfofreitas]

As I understand, the data grid and date pickers will have each their own migration guide.

I think we could also* have an "MUI X migration page" combining both MD files, to be referenced in tweets, blogs and other announcements. A "landing page" for migration. Does that make sense to you?
Maybe we could add it to the "Introduction" section.

cc/ @flaviendelangle

[flaviendelangle]

I guess we have two options

1. We do like the core with a Migration section in the nav bar with a "home page" (equivalent of this page for the core) plus one page per product line (one for the pickers and one for the grid)

2. We do one page per product line in their own doc scope and we create a "home page" in the "Introduction" section

I prefer the first option

[joserodolfofreitas]

Yeah, thanks for pointing that out. I agree a navbar section is a good option, it'll likely get more attention than on introduction, plus we keep consistency with the core.
Let's move forward with that.

[m4theushw]

@joserodolfofreitas What should be the content structure of this homepage for migration? I don't think we have many topics to cover, like https://mui.com/material-ui/migration/migration-v4/, the main purpose are the breaking changes.

[joserodolfofreitas]

@m4theushw, it's fine that there isn't much content on this page. If it covers everything we need to migrate and it's short, it's perfect.
This is going to be a living page that we edit with each PR that adds a breaking change.