Implement extensible manifest for updates in Foundation.

foundation-core/src/main/kotlin/gay/pizza/foundation/concrete/ExtensibleManifest.kt

@@ -0,0 +1,60 @@
+package gay.pizza.foundation.concrete
+
+import kotlinx.serialization.Serializable
+
+/**
+ * The extensible update manifest format.
+ */
+@Serializable
+data class ExtensibleManifest(
+  /**
+   * The items the manifest describes.
+   */
+  val items: List<ExtensibleManifestItem>
+)
+
+/**
+ * An item in the update manifest.
+ */
+@Serializable
+data class ExtensibleManifestItem(
+  /**
+   * The name of the item.
+   */
+  val name: String,
+  /**
+   * The type of item.
+   */
+  val type: String,
+  /**
+   * The version of the item.
+   */
+  val version: String,
+  /**
+   * The dependencies of the item.
+   */
+  val dependencies: List<String>,
+  /**
+   * The files that are required to install the item.
+   */
+  val files: List<ExtensibleManifestItemFile>
+)
+
+/**
+ * A file built from the item.
+ */
+@Serializable
+data class ExtensibleManifestItemFile(
+  /**
+   * The name of the file.
+   */
+  val name: String,
+  /**
+   * A type of file.
+   */
+  val type: String,
+  /**
+   * The relative path to download the file.
+   */
+  val path: String
+)