Convert existing migrations from timestamp to versioned

db/migrations/00018_add_unique_constraint_blocks_node.sql

@@ -0,0 +1,7 @@
+-- +goose Up
+ALTER TABLE blocks
+  ADD CONSTRAINT node_id_block_number_uc UNIQUE (block_number, node_id);
+
+-- +goose Down
+ALTER TABLE blocks
+  DROP CONSTRAINT node_id_block_number_uc;