Add refinements to the AI onboarding flow (#33738)

This includes making sure that both the agent panel and Zed's edit
prediction have a consistent narrative when it comes to onboarding users
into the AI features, considering the possible different plans and
conditions (such as being signed in/out, account age, etc.)

Release Notes:

- N/A

---------

Co-authored-by: Bennet Bo Fenner <53836821+bennetbo@users.noreply.github.com>
Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>

crates/copilot/src/copilot.rs

@@ -209,8 +209,14 @@ impl Status {
         matches!(self, Status::Authorized)
     }
 
-    pub fn is_disabled(&self) -> bool {
-        matches!(self, Status::Disabled)
+    pub fn is_configured(&self) -> bool {
+        matches!(
+            self,
+            Status::Starting { .. }
+                | Status::Error(_)
+                | Status::SigningIn { .. }
+                | Status::Authorized
+        )
     }
 }