Feature theme augmentation

[rajzik]

• I have followed (at least) the PR section of the contributing guide.

Fixes: #1874

This PR will unify the approach to the material-ui monorepo see: https://github.com/mui-org/material-ui/tree/next/packages/material-ui-lab/src/themeAugmentation

I also added documentation for the theme augmentation as well as fixed component names to correspond with theme overrides.

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[oliviertassinari]

@rajzik Thanks for the effort. Note that we are working on merging the components into the lab in https://github.com/mui-org/core-plus-pickers. We will have to redo this pull request on https://github.com/mui-org/material-ui once the migration is completed.

[rajzik]

@oliviertassinari oh, nvm. If you need any help just let me know.

[oliviertassinari]

I will let you know :)

[rajzik]

@oliviertassinari is there any estimation when the migration will be done?

[oliviertassinari]

@dmtrKovalenko is making great progress. I think that so far, the main blocker is to reach a point where https://github.com/mui-org/core-plus-pickers/tree/next/packages/pickers is no longer included in the repository.

[oliviertassinari]

@rajzik Thanks for the effort! I believe we have solved the issue by moving the component in the lab.