Support 'limit' with show proxied queries

This truncates the output of `show proxied queries limit n` to n rows.

The truncation happens after our sorting so tha the top n rows are the
"most useful" ones as determined by our sorting.

Release-Note-Core: You can now limit the number of rows returned by
  `show proxied queries` by adding a 'limit n' clause.

Change-Id: I8b3f877f2c299f5daf139e9a8cab8ea9c0e1839e
Reviewed-on: https://gerrit.readyset.name/c/readyset/+/6265
Tested-by: Buildkite CI
Reviewed-by: Jason Brown <[email protected]>

Author: Luke Osborne

readyset-adapter/src/backend.rs

@@ -1804,6 +1804,7 @@ where
         &mut self,
         query_id: &Option<String>,
         only_supported: bool,
+        limit: Option<u64>,
     ) -> ReadySetResult<noria_connector::QueryResult<'static>> {
         let mut queries = self.state.query_status_cache.deny_list();
         if let Some(q_id) = query_id {
@@ -1898,6 +1899,10 @@ where
             }
         });
 
+        if let Some(limit) = limit {
+            data.truncate(limit as usize);
+        }
+
         Ok(noria_connector::QueryResult::from_owned(
             select_schema,
             vec![Results::new(data)],
@@ -2102,6 +2107,7 @@ where
                 self.show_proxied_queries(
                     &proxied_queries_options.query_id,
                     proxied_queries_options.only_supported,
+                    proxied_queries_options.limit,
                 )
                 .await
             }