Clickhouse: add select consistency (#2300)

### Overview
[A recent effort ](https://github.com/PeerDB-io/peerdb/pull/2256/files)
was made to improve PeerDB's ingestion performance into ClickHouse by
parallelizing the INSERT INTO SELECT queries which took data from the
raw table and put it into the final tables. Just before this step,
PeerDB moves data from S3 to the raw table.

### Problem
In this implementation, every insert runs on a new ClickHouse session -
which means the inserts could be running on different nodes/replicas. In
this case, there exists a non-zero chance (albeit very unliikely) that
the INSERT INTO SELECT does not read the rows in the raw table inserted
by the first step.
This is documented here:
https://clickhouse.com/docs/en/cloud/reference/shared-merge-tree#consistency

### Solution
This PR adds the setting `select_sequential_consistency = 1` in the
`Connect` function which we use for connecting to ClickHouse

flow/connectors/clickhouse/clickhouse.go

@@ -228,11 +228,12 @@ func Connect(ctx context.Context, env map[string]string, config *protos.Clickhou
 		tlsSetting.RootCAs = caPool
 	}
 
-	var settings clickhouse.Settings
+	// See: https://clickhouse.com/docs/en/cloud/reference/shared-merge-tree#consistency
+	settings := clickhouse.Settings{"select_sequential_consistency": uint64(1)}
 	if maxInsertThreads, err := peerdbenv.PeerDBClickHouseMaxInsertThreads(ctx, env); err != nil {
 		return nil, fmt.Errorf("failed to load max_insert_threads config: %w", err)
 	} else if maxInsertThreads != 0 {
-		settings = clickhouse.Settings{"max_insert_threads": maxInsertThreads}
+		settings["max_insert_threads"] = maxInsertThreads
 	}
 
 	conn, err := clickhouse.Open(&clickhouse.Options{