UI: Upgrade storybook (#10904)

* upgrade storybook

* add changelog

changelog/10904.txt

@@ -0,0 +1,3 @@
+```release-note:improvement
+ui: Upgrade Storybook from 5.3.19 to 6.1.17.
+```

ui/package.json

@@ -45,7 +45,7 @@
     "@glimmer/component": "^1.0.1",
     "@glimmer/tracking": "^1.0.0",
     "@hashicorp/structure-icons": "^1.3.0",
-    "@storybook/ember-cli-storybook": "^0.2.1",
+    "@storybook/ember-cli-storybook": "^0.3.0",
     "Duration.js": "icholy/Duration.js#golang_compatible",
     "autosize": "^4.0.0",
     "babel-eslint": "^10.1.0",
@@ -148,12 +148,12 @@
   },
   "optionalDependencies": {
     "@babel/core": "^7.12.3",
-    "@storybook/addon-knobs": "^5.3.19",
-    "@storybook/addon-links": "^5.3.19",
+    "@storybook/addon-knobs": "^6.1.17",
+    "@storybook/addon-links": "^6.1.17",
     "@storybook/addon-notes": "^5.3.19",
-    "@storybook/addon-viewport": "^5.3.19",
-    "@storybook/addons": "^5.3.19",
-    "@storybook/ember": "^5.3.19",
+    "@storybook/addon-viewport": "^6.1.17",
+    "@storybook/addons": "^6.1.17",
+    "@storybook/ember": "^6.1.17",
     "babel-loader": "^8.1.0",
     "jsdoc-to-markdown": "^5.0.0",
     "lint-staged": "^10.5.1"