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/client/src/client.rs

@@ -301,6 +301,13 @@ impl Status {
         matches!(self, Self::Connected { .. })
     }
 
+    pub fn is_signing_in(&self) -> bool {
+        matches!(
+            self,
+            Self::Authenticating | Self::Reauthenticating | Self::Connecting | Self::Reconnecting
+        )
+    }
+
     pub fn is_signed_out(&self) -> bool {
         matches!(self, Self::SignedOut | Self::UpgradeRequired)
     }