Feature Request: Allow customization of bubble / toolbar UI

[olavblj]

Problem:
Agentation block certain use cases with it's restrictive API. For instance, a system might rely on forensic detail level, this is currently not possible to ensure. It also would be nice to be able to customize the appearance in case you don't find the default icon intuitive, or you want to modify the menu appearance etc.

My specific proposal is:

type AgentationProps = {
  // ...all current fields
  showSettings: false,
  defaultSettings: {
    detailLevel: "forensic"  
  },
  appearance: // inspired by https://clerk.com/docs/nextjs/guides/customizing-clerk/appearance-prop/overview
}

I'm happy to open a PR for this if you welcome contributions.