Run default addressables build conditionally (#231)

* Add asmdef and Addressable content build in the builder

* Move asmdef content into its own directory

* Mark UnityBuilderAction as Editor-only

dist/default-build-script/Assets/Editor/UnityBuilderAction/UnityBuilderAction.asmdef

@@ -0,0 +1,23 @@
+{
+    "name": "UnityBuilderAction",
+    "references": [
+        "Unity.Addressables.Editor"
+    ],
+    "includePlatforms": [
+        "Editor"
+    ],
+    "excludePlatforms": [],
+    "allowUnsafeCode": false,
+    "overrideReferences": false,
+    "precompiledReferences": [],
+    "autoReferenced": true,
+    "defineConstraints": [],
+    "versionDefines": [
+        {
+            "name": "com.unity.addressables",
+            "expression": "1.0.0",
+            "define": "USE_ADDRESSABLES"
+        }
+    ],
+    "noEngineReferences": false
+}