feat: Add other tasks from chapter 6

sql/schema/004_refresh_token.sql

@@ -0,0 +1,12 @@
+-- +goose Up
+CREATE TABLE refresh_tokens (
+    token TEXT PRIMARY KEY,
+    created_at TIMESTAMP NOT NULL,
+    updated_at TIMESTAMP NOT NULL,
+    user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    expires_at TIMESTAMP,
+    revoked_at TIMESTAMP
+);
+
+-- +goose Down
+DROP TABLE refresh_tokens;