adapter cloudflare overwrites user’s _routes.json without warning

[eltigerchino]

Describe the problem

It may not be obvious that you have to configure the cloudflare pages _routes.json in the svelte config if you’re coming from the cloudfare docs. e.g. #12264

Describe the proposed solution

The adapter should throw an error when building so the user configures it in svelte config instead

Alternatives considered

No response

Importance

nice to have

Additional Information

No response