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/k8s/collab.template.yml

@@ -134,6 +134,11 @@ spec:
                 secretKeyRef:
                   name: anthropic
                   key: api_key
+            - name: ANTHROPIC_STAFF_API_KEY
+              valueFrom:
+                secretKeyRef:
+                  name: anthropic
+                  key: staff_api_key
             - name: GOOGLE_AI_API_KEY
               valueFrom:
                 secretKeyRef: