Add shared MQTT client and ResourceManagement-based MQTT integration service

[1nf0rmagician]

Summary

• We propose adding:
  • A shared, reusable MQTT client service configured from appsettings, to be registered in the service collection and usable across multiple features.
  • A Resource MQTT integration service that uses IResourceManagement and IResourceManagementChanges to publish resource events and handle subscriptions via the shared MQTT client.
  • A design that allows future reuse of the same MQTT client in a similar service built on IProductManagement.

Motivation

• Based on Add abstractions for resources synchronized throughout multiple MORYX applications #656 and Expose ResourceChanged notifications from ResourceManagement as a non-breaking facade extension #657, we want to allow applications to share resources throughout multiple MORYX instances
• One provider of the synchronization itself can be MQTT, this is what the feature request proposes

Proposed Design

• Configuration

  • Add a typed options class bound from appsettings:
  • Section: Mqtt
  • Properties:
    • Host (string)
    • Port (int)
    • ClientId (string)
    • Username (string, optional)
    • Password (string, optional/secret)
    • UseTls (bool, default false)
    • CleanSession (bool, default true)
    • KeepAliveSeconds (int, default 30)
    • ReconnectDelaySeconds (int, default 5)
    • TopicPrefix (string, default "moryx")
    • QoS (int 0..2, default 1)
    • Retain (bool, default false)

• Shared MQTT client abstraction IMqttClientService

  • Lifetime: Singleton, registered in DI, and also implements IHostedService for lifecycle management (connect on start, disconnect on stop).
  • Uses MQTTnet client options built from MqttOptions to handle connection, TLS, credentials, keep-alive, and auto-reconnect logic.
  • Logs connection state changes and errors.
  • Designed for reuse by a future ProductManagement MQTT service.

• Resource MQTT integration service

  • A BackgroundService (or IHostedService) that depends on:
    • IResourceManagement (from ResourceManagementFacade)
    • IResourceManagementChanges (from ResourceManagementFacade)
    • IMqttBus
    • IOptions
    • ILogger
  • Responsibilities:
    • Subscribe to IResourceManagement events:
      • ResourceAdded
      • ResourceRemoved
    • Publish event messages to MQTT topics. Suggested topics:
      • {TopicPrefix}/resources//added
      • {TopicPrefix}/resources//removed
  • Payload: json serialization of resource object (using System.Text.Json with Web defaults)
    • respect ISerializable interface and IResourceSerializable interface for resources
  • Ensure ValidateHealthState is respected by only accessing facade operations in event callbacks or on Start when module is healthy.

• Future extension: Product MQTT integration service

  • A separate service (not part of this change set, but supported by the shared IMqttClientService) that would:
  • Depend on IProductManagement
  • Reuse same IMqttClientService instance and configuration.

• Registration

  • Provide an extension method to register everything in DI, similar to AddControllers