feat(core): support horizontally scaling platform postgres

.github/scripts/postgres-primary-init.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+set -e
+
+echo "Setting up replication user..."
+psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" --dbname "$POSTGRES_DB" <<-EOSQL
+    DO \$\$
+    BEGIN
+        IF NOT EXISTS (SELECT FROM pg_catalog.pg_roles WHERE rolname = 'replicator') THEN
+            CREATE ROLE replicator WITH REPLICATION PASSWORD 'replicator_password' LOGIN;
+        END IF;
+    END
+    \$\$;
+    GRANT CONNECT ON DATABASE $POSTGRES_DB TO replicator;
+EOSQL
+
+# Allow replication from same Docker network using 'samenet' keyword
+# This automatically matches any address in subnets the server is connected to
+echo "host replication replicator samenet md5" >> "${PGDATA}/pg_hba.conf"
+echo "Replication user configured"