assistant2: Setup storybook (#11228)

This PR sets up the `assistant2` crate with the storybook so that UI
elements can be iterated on in isolation.

To start, we have some stories for the `ChatMessage` component:

```sh
cargo run -p storybook -- components/assistant_chat_message
```

<img width="1233" alt="Screenshot 2024-04-30 at 5 20 03 PM"
src="https://github.com/zed-industries/zed/assets/1486634/510967ea-0e9b-4fa9-94fb-421ee74bcc45">

Release Notes:

- N/A

crates/storybook/Cargo.toml

@@ -14,6 +14,7 @@ path = "src/storybook.rs"
 
 [dependencies]
 anyhow.workspace = true
+assistant2 = { workspace = true, features = ["stories"] }
 clap = { workspace = true, features = ["derive", "string"] }
 collab_ui = { workspace = true, features = ["stories"] }
 ctrlc = "3.4"

crates/storybook/src/story_selector.rs

@@ -12,6 +12,7 @@ use ui::prelude::*;
 #[derive(Debug, PartialEq, Eq, Clone, Copy, strum::Display, EnumString, EnumIter)]
 #[strum(serialize_all = "snake_case")]
 pub enum ComponentStory {
+    AssistantChatMessage,
     AutoHeightEditor,
     Avatar,
     Button,
@@ -42,6 +43,9 @@ pub enum ComponentStory {
 impl ComponentStory {
     pub fn story(&self, cx: &mut WindowContext) -> AnyView {
         match self {
+            Self::AssistantChatMessage => {
+                cx.new_view(|_cx| assistant2::ui::ChatMessageStory).into()
+            }
             Self::AutoHeightEditor => AutoHeightEditorStory::new(cx).into(),
             Self::Avatar => cx.new_view(|_| ui::AvatarStory).into(),
             Self::Button => cx.new_view(|_| ui::ButtonStory).into(),