Add post logout redirect uri

> Please provide us with the following information:
> ---------------------------------------------------------------

### This issue is for a: (mark with an `x`)
```
- [ ] bug report -> please search issues before submitting
- [x] feature request
- [ ] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)
```

### Expected/desired behavior
> Ability to have custom redirect endpoint after logout that is different from redirect uri

### OS and Version?
> Windows 8, 10, or 11. Linux (which distribution). macOS (Mojave? Catalina? Big Sur? Monterey?)
Linux

### Versions
>

### Mention any other details that might be useful
Can be the same configuration option as REDIRECT_URI but for post logout. I have a custom combo architecture of Flask and Dash and I need to override the logout page.

> ---------------------------------------------------------------
> Thanks! We'll be in touch soon.

No file, test, or entry point is named. Start by locating the sample's logout flow and current REDIRECT_URI configuration, then define how a separate post-logout redirect option should work with the Flask and Dash combination; done means logout can use a custom endpoint distinct from the existing redirect URI.

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