refactor: store migrator

store/migration/postgres/prod/0.20/00_reaction.sql

@@ -0,0 +1,9 @@
+-- reaction
+CREATE TABLE reaction (
+  id SERIAL PRIMARY KEY,
+  created_ts BIGINT NOT NULL DEFAULT EXTRACT(EPOCH FROM NOW()),
+  creator_id INTEGER NOT NULL,
+  content_id TEXT NOT NULL,
+  reaction_type TEXT NOT NULL,
+  UNIQUE(creator_id, content_id, reaction_type)
+);