collab: Make metrics_id required in LlmTokenClaims (#21771)

This PR makes the `metrics_id` field on the `LlmTokenClaims` required,
as we always have one in practice.

Release Notes:

- N/A

crates/collab/src/api/billing.rs

@@ -130,7 +130,7 @@ async fn update_billing_preferences(
 
     SnowflakeRow::new(
         "Spend Limit Updated",
-        Some(user.metrics_id),
+        user.metrics_id,
         user.admin,
         None,
         json!({

crates/collab/src/api/events.rs

@@ -1593,7 +1593,7 @@ pub struct SnowflakeRow {
 impl SnowflakeRow {
     pub fn new(
         event_type: impl Into<String>,
-        metrics_id: Option<Uuid>,
+        metrics_id: Uuid,
         is_staff: bool,
         system_id: Option<String>,
         event_properties: serde_json::Value,
@@ -1602,7 +1602,7 @@ impl SnowflakeRow {
             time: chrono::Utc::now(),
             event_type: event_type.into(),
             device_id: system_id,
-            user_id: metrics_id.map(|id| id.to_string()),
+            user_id: Some(metrics_id.to_string()),
             insert_id: Some(uuid::Uuid::new_v4().to_string()),
             event_properties,
             user_properties: Some(json!({"is_staff": is_staff})),