feat: Add versioning support to EssentialsConfig

Introduce `Versions` property in `EssentialsConfig` to hold version information.
Add `VersionData` class for Essentials and package versions, and `NugetVersion` class for individual package details.
Retain and document `SystemTemplateConfigs` class.

src/PepperDash.Essentials.Core/Config/Essentials/EssentialsConfig.cs

@@ -85,6 +85,11 @@ namespace PepperDash.Essentials.Core.Config
 
         public List<DeviceConfig> Rooms { get; set; }
 
+        /// <summary>
+        /// Gets or sets the Versions
+        /// </summary>
+        public VersionData Versions { get; set; }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="EssentialsConfig"/> class.
         /// </summary>
@@ -95,6 +100,50 @@ namespace PepperDash.Essentials.Core.Config
         }
 	}
 
+    /// <summary>
+    /// Represents version data for Essentials and its packages
+    /// </summary>
+    public class VersionData
+    {
+        /// <summary>
+        /// Gets or sets the Essentials version
+        /// </summary>
+        [JsonProperty("essentials")]
+        public NugetVersion Essentials { get; set; }
+
+        /// <summary>
+        /// Gets or sets the list of Packages
+        /// </summary>
+        [JsonProperty("packages")]
+        public List<NugetVersion> Packages { get; set; }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="VersionData"/> class.
+        /// </summary>
+        public VersionData()
+        {
+            Packages = new List<NugetVersion>();
+        }
+    }
+
+    /// <summary>
+    /// Represents a NugetVersion
+    /// </summary>
+    public class NugetVersion
+    {
+        /// <summary>
+        /// Gets or sets the Version
+        /// </summary>
+        [JsonProperty("version")]
+        public string Version { get; set; }
+
+        /// <summary>
+        /// Gets or sets the PackageId
+        /// </summary>
+        [JsonProperty("packageId")]
+        public string PackageId { get; set; }
+    }
+
     /// <summary>
     /// Represents a SystemTemplateConfigs
     /// </summary>