Introduce staff-only inline completion provider (#21739)

Release Notes:

- N/A

---------

Co-authored-by: Thorsten Ball <mrnugget@gmail.com>
Co-authored-by: Bennet <bennet@zed.dev>
Co-authored-by: Thorsten <thorsten@zed.dev>

crates/collab/src/lib.rs

@@ -180,6 +180,9 @@ pub struct Config {
     pub anthropic_api_key: Option<Arc<str>>,
     pub anthropic_staff_api_key: Option<Arc<str>>,
     pub llm_closed_beta_model_name: Option<Arc<str>>,
+    pub prediction_api_url: Option<Arc<str>>,
+    pub prediction_api_key: Option<Arc<str>>,
+    pub prediction_model: Option<Arc<str>>,
     pub zed_client_checksum_seed: Option<String>,
     pub slack_panics_webhook: Option<String>,
     pub auto_join_channel_id: Option<ChannelId>,
@@ -230,6 +233,9 @@ impl Config {
             anthropic_api_key: None,
             anthropic_staff_api_key: None,
             llm_closed_beta_model_name: None,
+            prediction_api_url: None,
+            prediction_api_key: None,
+            prediction_model: None,
             clickhouse_url: None,
             clickhouse_user: None,
             clickhouse_password: None,