Add create combined table migration

week_8/examples/posts_and_comments/20210303T143000-create_combines_table.sql

+-- create table posts (
+--   id INT AUTO_INCREMENT PRIMARY KEY,
+--   slug VARCHAR(30) NOT NULL,
+--   title VARCHAR(255) NOT NULL,
+--   body TEXT
+-- );
+--
+-- create table comments (
+--   id INT AUTO_INCREMENT PRIMARY KEY,
+--   post_id INT,
+--   body TEXT,
+--   author VARCHAR(30),
+--   FOREIGN KEY(post_id) REFERENCES posts(id)
+-- );
+
+create table posts_and_comments (
+    id INT AUTO_INCREMENT PRIMARY KEY,
+    body TEXT,
+    slug VARCHAR(30) NOT NULL,
+    title VARCHAR(255) NOT NULL,
+    post_id INT,
+    author VARCHAR(30)
+)