collab: Use a separate Anthropic API key for Zed staff (#16128)

This PR makes it so Zed staff can use a separate Anthropic API key for
the LLM service.

We also added an `is_staff` column to the `usages` table so that we can
exclude staff usage from the "active users" metrics that influence the
rate limits.

Release Notes:

- N/A

---------

Co-authored-by: Max <max@zed.dev>

crates/collab/src/llm.rs

@@ -171,11 +171,19 @@ async fn perform_completion(
 
     let stream = match params.provider {
         LanguageModelProvider::Anthropic => {
-            let api_key = state
-                .config
-                .anthropic_api_key
-                .as_ref()
-                .context("no Anthropic AI API key configured on the server")?;
+            let api_key = if claims.is_staff {
+                state
+                    .config
+                    .anthropic_staff_api_key
+                    .as_ref()
+                    .context("no Anthropic AI staff API key configured on the server")?
+            } else {
+                state
+                    .config
+                    .anthropic_api_key
+                    .as_ref()
+                    .context("no Anthropic AI API key configured on the server")?
+            };
 
             let mut request: anthropic::Request =
                 serde_json::from_str(&params.provider_request.get())?;
@@ -473,6 +481,7 @@ impl<S> Drop for TokenCountingStream<S> {
                 .db
                 .record_usage(
                     claims.user_id as i32,
+                    claims.is_staff,
                     provider,
                     &model,
                     input_token_count,