Add configuration system with MQTT topic and board ID support

[ajlennon]

Summary

This PR adds a comprehensive configuration system for the CGA Coordinate Mapping application, making MQTT topics and other settings configurable via appsettings.json.

Changes

• Configuration System: Added Microsoft.Extensions.Configuration packages and AppConfig.cs for type-safe configuration loading
• Hardware ID Detection: Created HardwareId.cs to detect unique board identifiers (machine-id, DMI UUID, MAC address, or hostname)
• MQTT Configuration: Made all MQTT settings configurable (server, port, topics, credentials, keepalive, etc.)
• Board ID Placeholder: Added support for {$BoardID} placeholder in topic strings for board-specific topics
• Default Values: Topics default to original hardcoded values (DotnetMQTT/Test/in and DotnetMQTT/Test/out)
• Auto Client ID: MQTT client ID automatically generated from hardware ID if not configured

Configuration File

• appsettings.json added with all configurable settings
• Comments included explaining board ID placeholder usage
• Environment variable override support (e.g., MQTT__ReceiveTopic)

Example Usage

To use board-specific topics, update appsettings.json:

{
  "MQTT": {
    "ReceiveTopic": "uwb/{$BoardID}/network/in",
    "SendTopic": "uwb/{$BoardID}/coordinates/out"
  }
}

The {$BoardID} placeholder will be automatically replaced with the hardware-based MQTT client ID (e.g., UwbManager-machine-xxx).

Testing

• ✅ Build succeeds
• ✅ Configuration loads correctly
• ✅ Placeholder resolution works
• ✅ Default topics match original hardcoded values
• ✅ Hardware ID detection works (falls back through multiple methods)

Reviewer

@Jen42 - Please review this PR when you have a chance.