[Doc] Update Admin and Routing docs to encourage using a Data Router

[smeng9]

Problem

Current docs is outdated, does not work data APIs

React-router recommends user to update to use new API.

Solution

We should let user use warnWhenUnsavedChanges when they perform their setup with latest best practice

How To Test

Describe the steps required to test the changes

Additional Checks

• The PR targets master for a bugfix, or next for a feature
• The PR includes unit tests (if not possible, describe why)
• The PR includes one or several stories (if not possible, describe why)
• The documentation is up to date

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[fzaninotto]

Thanks for your PR.

The current doc mention a way to use a regular router, and it works. It is true that if you want to use an data router, the doc needs to be updated. But I'm not sure that replacing the doc with the data router version is the best thing to do, as the setup is a bit more complicate din this case.

Any second opinion on that?

[slax57]

@fzaninotto Using a regular router works, sure, except regarding the warnWhenUnsavedChanges feature. This may come as a (bad) suprise to users willing to use that feature in the future.

Hence, I would agree with @smeng9 that it's best to encourage using a data router as soon as possible in the docs, to minimize the chances of users running into the issue of the non-working warnWhenUnsavedChanges feature.

[fzaninotto]

You've convinced me! Let's merge this.

[slax57]

Thanks!