feat: upgrade application to .NET 10

Preserve configuration defaults with the .NET 10 binder and update
dependencies, Docker builds, CI, and test tooling.

CaddyManager.Services/Configurations/ConfigurationsService.cs

@@ -19,6 +19,18 @@ public class ConfigurationsService(IConfiguration configuration) : IConfiguratio
         else if (section.EndsWith("Configuration"))
             section = section[..^"Configuration".Length];
         
-        return configuration.GetSection(section).Get<T>() ?? Activator.CreateInstance<T>();
+        var result = configuration.GetSection(section).Get<T>();
+        var defaults = Activator.CreateInstance<T>();
+
+        if (result is null) return defaults;
+
+        // The .NET 10 binder writes nulls over property initialisers, so put the defaults back
+        foreach (var property in typeof(T).GetProperties())
+        {
+            if (property is { CanRead: true, CanWrite: true } && property.GetValue(result) is null)
+                property.SetValue(result, property.GetValue(defaults));
+        }
+
+        return result;
     }
 }