Engage endpoint

server/migrations/0005_engagements_table.sql

@@ -0,0 +1,7 @@
+CREATE TABLE IF NOT EXISTS engagements (
+    user_id BIGINT NOT NULL,
+    post_id BIGINT NOT NULL,
+    FOREIGN KEY (user_id) REFERENCES users (id),
+    FOREIGN KEY (post_id) REFERENCES posts (id),
+    PRIMARY KEY (user_id, post_id)
+);