[Network] Expose Azure Firewall for Containers (AFC) managed Firewall Policy on az network firewall policy

### Preconditions

- [x] No need to upgrade Python SDK or the Python SDK is ready.

### Related command

az network firewall policy create
az network firewall policy update
az network firewall policy show

### Resource Provider

Microsoft.Network/firewallPolicies

### Description of Feature or Work Requested

Expose the afcManaged capability on an Azure Firewall Policy (Azure Firewall for Containers), matching the new PowerShell support (PR #30006).

afcManaged marks a firewall policy as managed by AFC (Azure Firewall for Containers). The CLI should:

- surface afcManaged in az network firewall policy show output, and

- expose it as a parameter on az network firewall policy create / update if it is settable per the swagger (exact property/param name and shape should follow the spec).

Property name, type, and whether it is read-only vs settable are defined in the swagger PR below and mirrored by the PowerShell change.

### Minimum API Version Required

2025-09-01

### Swagger PR link / SDK link

https://github.com/Azure/azure-rest-api-specs/pull/44867

### Request Example

See the firewall policy examples in the swagger PR: https://github.com/Azure/azure-rest-api-specs/pull/44867/files

### Target Date

2026-08-30

### PM Contact

Suren.Jamiyanaa@microsoft.com

### Engineer Contact

samankal@microsoft.com

### Additional context

- PowerShell PR (reference behavior): https://github.com/Azure/azure-powershell/pull/30006

- Location: azure-firewall extension (same place as az network firewall policy)