tsk-8: Create Message endpoint (#15)

Closes #8

Reviewed-on: phoenix/textsender-api#15
Co-authored-by: phoenix <kundeng00@pm.me>
Co-committed-by: phoenix <kundeng00@pm.me>

migrations/schema.sql

@@ -8,3 +8,8 @@ CREATE TABLE contacts (
     user_id UUID NOT NULL
 );
 
+CREATE TABLE messages (
+    id UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
+    content TEXT NOT NULL,
+    user_id UUID NOT NULL
+);