Update SDK namespace from applink to appnetwork

[deveshdama]

Changed SDK package names to use 'appnetwork' instead of 'applink' following namespace approval.

• .NET: Azure.ResourceManager.AppNetwork
• Java: com.azure.resourcemanager.appnetwork
• Go: sdk/resourcemanager/appnetwork/armappnetwork
• JS: @azure/arm-appnetwork
• Python: azure-mgmt-appnetwork

RP namespace Microsoft.AppLink remains unchanged.

Approval - https://github.com/Azure/azure-sdk-pr/issues/2568

SDK configuration pull request

Purpose of this PR

• Make changes to the SDK configuration only when there are no modifications to the API specification, eliminating the need for an ARM or Stewardship Board API review.

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Pull request overview

Updates the SDK emitter configuration for the AppLink management TypeSpec project to use the newly approved AppNetwork SDK namespaces/package names, while keeping the RP namespace (Microsoft.AppLink) unchanged.

Changes:

• Updated the C# management namespace to Azure.ResourceManager.AppNetwork.
• Updated Python/Java/TS/Go emitter output directories and package/module/namespace identifiers from applink to appnetwork.
• Updated the default service-dir parameter from sdk/applink to sdk/appnetwork.