chore: implement Internet Identity example recommendations

[krpeacock]

Here are some recommendations I have on best practices in the II example project.

Important and functional changes

• AuthClient create should not be invoked during the login flow
  • Awaiting async behavior during the click event leads browsers to treat the interaction as a popup and reject it. This is a particular footgun for Safari mobile
  • fix: move AuthClient.create() into the global scope, and then update the Actor globally
• Disable login button and greet button until the authClient is ready
• Remove Promise wrapping of login
  • I get that await is fancy, but the actual browser API is based around callbacks and events, and onSuccess and onError are adequate.
  • Note: I would also accept the wrapping if it at least rejected in the onError callback

Less important (semantic HTML, a11y, and style)

• Using window.greetActor and window.authClient instead of local variables so new devs can play with the objects in the console. We DO NOT have to accept this change - it's just an idea I had
• The form elements are unnecessary without input elements, and don't add any semantic value. I prefer <button type="button"> over an empty form, and then we don't need to handle submit events