[docs] Update API design approach guide

[oliviertassinari]

The content of this guide https://mui.com/material-ui/guides/api/ is getting outdated, it's not longer in sync with how we design APIs. We raised in https://github.com/mui/material-ui/issues/34895#issuecomment-1304205535 that it could be great to update it. The value would be:

• For MUI
  • To create more consistent APIs
  • To know why specific APIs exist. It's going to be hard two years from now to find the GitHub or Notion pages where we agreed on the given APIs and why. This will avoid making unnecessary changes to how we design APIs because we are missing the full context of the constraints with the current guidelines.
• For the community
  • To know how best to extend MUI.

[flaviendelangle]

Related to https://github.com/mui/material-ui/issues/31745