Send up Zed version with edit prediction and completion requests (#30136)

This PR makes it so we send up an `x-zed-version` header with the
client's version when making a request to llm.zed.dev for edit
predictions and completions.

Release Notes:

- N/A

crates/zeta/src/zeta.rs

@@ -55,7 +55,7 @@ use workspace::notifications::{ErrorMessagePrompt, NotificationId};
 use worktree::Worktree;
 use zed_llm_client::{
     EXPIRED_LLM_TOKEN_HEADER_NAME, MINIMUM_REQUIRED_VERSION_HEADER_NAME, PredictEditsBody,
-    PredictEditsResponse,
+    PredictEditsResponse, ZED_VERSION_HEADER_NAME,
 };
 
 const CURSOR_MARKER: &'static str = "<|user_cursor_is_here|>";
@@ -754,6 +754,7 @@ and then another
                 let request = request_builder
                     .header("Content-Type", "application/json")
                     .header("Authorization", format!("Bearer {}", token))
+                    .header(ZED_VERSION_HEADER_NAME, app_version.to_string())
                     .body(serde_json::to_string(&body)?.into())?;
 
                 let mut response = http_client.send(request).await?;