feat(devx): introduce storybook

First shot at introducing storybook, with stories for the keycloak
theme pages already in the repo.

.storybook/preview.js

@@ -0,0 +1,9 @@
+export const parameters = {
+  actions: { argTypesRegex: "^on[A-Z].*" },
+  controls: {
+    matchers: {
+      color: /(background|color)$/i,
+      date: /Date$/,
+    },
+  },
+}