Add platformReleaseChannel property to Webapp Site model

[sarsharma]

Add platformReleaseChannel property to Site model

Description

This PR adds the platformReleaseChannel property to the Site resource model
The Azure App Service platform supports a release channel configuration (Latest, Standard, or Extended) that controls the order in which platform updates are applied to web apps:

Related PRs

• Azure CLI: Azure/azure-cli#32811 — az webapp update --platform-release-channel support

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[github-actions]

API Change Check

APIView identified API level changes in this PR and created the following API reviews

Language	API Review for Package
Swagger	Microsoft.Web-AppService
JavaScript	@azure/arm-appservice
Java	com.azure.resourcemanager:azure-resourcemanager-appservice-generated
TypeSpec	Microsoft.Web
Go	sdk/resourcemanager/appservice/armappservice
Java	com.azure.resourcemanager:azure-resourcemanager-appservice