Use correct arch when publishing app

[Gérald Barré (meziantou)]

Jira issue link: FENG-905

[Copilot]

Pull Request Overview

This PR updates the Dockerfile to support multi-architecture builds by dynamically selecting the correct .NET runtime identifier based on the target platform. Instead of hardcoding the x64 architecture, the build process now conditionally publishes for either amd64 (x64) or arm64 architectures.

• Replaces hardcoded linux-musl-x64 runtime identifier with conditional logic
• Adds ARG TARGETPLATFORM to capture the build platform during Docker build
• Uses shell conditional to select appropriate runtime identifier (linux-musl-x64 or linux-musl-arm64)

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