collab: Fix writing LLM rate limit events to Clickhouse (#16367)

This PR fixes the writing of LLM rate limit events to Clickhouse.

We had a table in the table name: `llm_rate_limits` instead of
`llm_rate_limit_events`.

I also extracted a helper function to write to Clickhouse so we can use
it anywhere we need to.

Release Notes:

- N/A

crates/collab/src/clickhouse.rs

@@ -0,0 +1,28 @@
+use serde::Serialize;
+
+/// Writes the given rows to the specified Clickhouse table.
+pub async fn write_to_table<T: clickhouse::Row + Serialize + std::fmt::Debug>(
+    table: &str,
+    rows: &[T],
+    clickhouse_client: &clickhouse::Client,
+) -> anyhow::Result<()> {
+    if rows.is_empty() {
+        return Ok(());
+    }
+
+    let mut insert = clickhouse_client.insert(table)?;
+
+    for event in rows {
+        insert.write(event).await?;
+    }
+
+    insert.end().await?;
+
+    let event_count = rows.len();
+    log::info!(
+        "wrote {event_count} {event_specifier} to '{table}'",
+        event_specifier = if event_count == 1 { "event" } else { "events" }
+    );
+
+    Ok(())
+}