[Stepper] Add cutomization example

[oliviertassinari]

The new example

The baseline

The target (from Qonto)

[mui-pr-bot]

Details of bundle changes.

Comparing: bff38c1...54014d6

bundle	parsed diff	gzip diff	prev parsed	current parsed	prev gzip	current gzip
@material-ui/core	-0.02%	-0.01%	331,378	331,314	90,885	90,876
@material-ui/core/Paper	0.00%	0.00%	69,177	69,177	20,528	20,528
@material-ui/core/Paper.esm	0.00%	0.00%	62,047	62,047	19,208	19,208
@material-ui/core/Popper	0.00%	0.00%	29,182	29,182	10,427	10,427
@material-ui/core/Textarea	0.00%	0.00%	5,759	5,759	2,367	2,367
@material-ui/core/TrapFocus	0.00%	0.00%	3,806	3,806	1,602	1,602
@material-ui/core/styles/createMuiTheme	0.00%	0.00%	16,390	16,390	5,825	5,825
@material-ui/core/useMediaQuery	0.00%	0.00%	3,221	3,221	1,314	1,314
@material-ui/lab	0.00%	0.00%	141,987	141,987	43,790	43,790
@material-ui/styles	0.00%	0.00%	51,886	51,886	15,339	15,339
@material-ui/system	0.00%	0.00%	15,761	15,761	4,380	4,380
Button	0.00%	0.00%	79,460	79,460	24,301	24,301
Modal	0.00%	0.00%	14,961	14,961	5,221	5,221
Portal	0.00%	0.00%	3,579	3,579	1,566	1,566
Rating	0.00%	0.00%	70,667	70,667	22,064	22,064
Slider	0.00%	0.00%	75,061	75,061	23,277	23,277
colorManipulator	0.00%	0.00%	3,904	3,904	1,543	1,543
docs.landing	0.00%	0.00%	52,056	52,056	13,831	13,831
docs.main	0.00%	0.00%	606,828	606,828	194,402	194,402
packages/material-ui/build/umd/material-ui.production.min.js	-0.02%	-0.01%	299,997	299,933	86,200	86,191

Generated by 🚫 dangerJS against 54014d6