Use url type for endpoint parameter in Azure Core Data Plane Service playground sample

[Copilot]

The playground sample was using endpoint: string instead of endpoint: url in the @server decorator, inconsistent with best practices and other samples throughout the codebase.

Changes

• Updated packages/typespec-azure-playground-website/samples/azure-core.tsp to use endpoint: url

 @server(
   "{endpoint}/widget",
   "Contoso Widget APIs",
   {
-    endpoint: string,
+    endpoint: url,
   }
 )

This aligns with the pattern used in documentation and test files across the repository.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Default data plane service in playground should use a url endpoint</issue_title>
<issue_description>```@server(
"{endpoint}/widget",
"Contoso Widget APIs",
{
/**
Supported Widget Services endpoints (protocol and hostname, for example:
https://westus.api.widget.contoso.com).
*/
endpoint: string,
}
)

Is there any reason to define this as a string? I believe the best practice is to use `url`.

[Playground Link](https://azure.github.io/typespec-azure/playground/?sample=Azure+Core+Data+Plane+Service&options=%7B%22linterRuleSet%22%3A%7B%22extends%22%3A%5B%22%40azure-tools%2Ftypespec-azure-rulesets%2Fdata-plane%22%5D%7D%7D&vs=%7B%7D)</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes Default data plane service in playground should use a url endpoint #3838

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[azure-sdk]

No changes needing a change description found.

[azure-sdk]

You can try these changes here

🛝 Playground	🌐 Website

[lmazuel]

Makes sense to me