[docs-infra] Force git diff to reset tabs origin

[oliviertassinari]

Summary

Create a new markdown lint rule so that git diff have to reset their tabs/spacing at the origin, meaning to go from:

+    foo() {
+      bar;

to:

+foo() {
+  bar;

Examples

Prior work was done around this in https://github.com/mui/material-ui/blob/master/packages/markdownlint-rule-mui/git-diff.js. This rule is here to make sure that the git diff we write has the correct format.

This issue is about a new rule as it's stylistic.

Motivation

Avoid the need to have comments like mui/mui-x#15575 (comment)

Search keywords: -