[proxy] chore: allow bypassing empty params to /sql endpoint (#9827)

## Problem

```
curl -H "Neon-Connection-String: postgresql://neondb_owner:PASSWORD@ep-autumn-rain-a58lubg0.us-east-2.aws.neon.tech/neondb?sslmode=require" https://ep-autumn-rain-a58lubg0.us-east-2.aws.neon.tech/sql -d '{"query":"SELECT 1","params":[]}'
```

For such a query, I also need to send `params`. Do I really need it?

## Summary of changes
I've marked `params` as optional

proxy/src/serverless/sql_over_http.rs

@@ -48,6 +48,7 @@ use crate::usage_metrics::{MetricCounter, MetricCounterRecorder};
 struct QueryData {
     query: String,
     #[serde(deserialize_with = "bytes_to_pg_text")]
+    #[serde(default)]
     params: Vec<Option<String>>,
     #[serde(default)]
     array_mode: Option<bool>,
@@ -1105,3 +1106,63 @@ impl Discard<'_> {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_payload() {
+        let payload = "{\"query\":\"SELECT * FROM users WHERE name = ?\",\"params\":[\"test\"],\"arrayMode\":true}";
+        let deserialized_payload: Payload = serde_json::from_str(payload).unwrap();
+
+        match deserialized_payload {
+            Payload::Single(QueryData {
+                query,
+                params,
+                array_mode,
+            }) => {
+                assert_eq!(query, "SELECT * FROM users WHERE name = ?");
+                assert_eq!(params, vec![Some(String::from("test"))]);
+                assert!(array_mode.unwrap());
+            }
+            Payload::Batch(_) => {
+                panic!("deserialization failed: case with single query, one param, and array mode")
+            }
+        }
+
+        let payload = "{\"queries\":[{\"query\":\"SELECT * FROM users0 WHERE name = ?\",\"params\":[\"test0\"], \"arrayMode\":false},{\"query\":\"SELECT * FROM users1 WHERE name = ?\",\"params\":[\"test1\"],\"arrayMode\":true}]}";
+        let deserialized_payload: Payload = serde_json::from_str(payload).unwrap();
+
+        match deserialized_payload {
+            Payload::Batch(BatchQueryData { queries }) => {
+                assert_eq!(queries.len(), 2);
+                for (i, query) in queries.into_iter().enumerate() {
+                    assert_eq!(
+                        query.query,
+                        format!("SELECT * FROM users{i} WHERE name = ?")
+                    );
+                    assert_eq!(query.params, vec![Some(format!("test{i}"))]);
+                    assert_eq!(query.array_mode.unwrap(), i > 0);
+                }
+            }
+            Payload::Single(_) => panic!("deserialization failed: case with multiple queries"),
+        }
+
+        let payload = "{\"query\":\"SELECT 1\"}";
+        let deserialized_payload: Payload = serde_json::from_str(payload).unwrap();
+
+        match deserialized_payload {
+            Payload::Single(QueryData {
+                query,
+                params,
+                array_mode,
+            }) => {
+                assert_eq!(query, "SELECT 1");
+                assert_eq!(params, vec![]);
+                assert!(array_mode.is_none());
+            }
+            Payload::Batch(_) => panic!("deserialization failed: case with only one query"),
+        }
+    }
+}