[Feature] Fleet: Support for Azure Custom Policies in Azure Kubernetes Fleet

**Is your feature request related to a problem? Please describe.**

Currently, Azure Fleet is designed to bypass Azure custom policies and only enforce built-in policies. This limitation restricts organizations from applying tailored governance and compliance rules that are critical to their operational and security requirements. As a result, teams relying on custom policies for resource control and auditing are unable to leverage Azure Fleet effectively.

**Describe the solution you'd like**

We would like Azure Fleet to support the evaluation and enforcement of Azure custom policies alongside built-in policies. This would allow organizations to maintain consistent governance across their environments and utilize Fleet for broader compliance scenarios. Ideally, this support should include:

• Full compatibility with custom policy definitions.
• Visibility into policy compliance results within Fleet.
• Logging and alerting for custom policy violations.

**Additional context**

Supporting custom policies would significantly enhance Fleet’s flexibility and adoption across enterprise environments.