Break ground on assistant2 (#21109)

This PR breaks ground on a new `assistant2` crate.

In order to see this new version of the assistant, both of the following
must be true:
1. The `assistant2` feature flag is enabled for your user
   - It is **not** currently enabled for all staff.
2. You are running a development build of Zed

The intent here is to enable the folks working on `assistant2` to
incrementally land work onto `main` without breaking use of the current
Assistant for anyone.

<img width="1136" alt="Screenshot 2024-11-23 at 10 46 08 AM"
src="https://github.com/user-attachments/assets/5723a13f-5be1-4486-9460-ead7329ba78e">

Release Notes:

- N/A

Cargo.lock

@@ -449,6 +449,19 @@ dependencies = [
  "zed_actions",
 ]
 
+[[package]]
+name = "assistant2"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "command_palette_hooks",
+ "feature_flags",
+ "gpui",
+ "proto",
+ "ui",
+ "workspace",
+]
+
 [[package]]
 name = "assistant_slash_command"
 version = "0.1.0"
@@ -15549,6 +15562,7 @@ dependencies = [
  "ashpd",
  "assets",
  "assistant",
+ "assistant2",
  "async-watch",
  "audio",
  "auto_update",