fix(@angular/cli): add missing defaults to optimization property

(cherry picked from commit 2195281)

Author: alan-agius4

packages/angular/cli/lib/config/schema.json

@@ -1239,6 +1239,7 @@
             },
             "optimization": {
               "description": "Enable optimization of the build output.",
+              "default": false,
               "oneOf": [
                 {
                   "type": "object",
@@ -1729,6 +1730,7 @@
             },
             "optimization": {
               "description": "Enables optimization of the build output.",
+              "default": false,
               "oneOf": [
                 {
                   "type": "object",