Chapter 12 review

[marquicodes]

These are the changes suggested after reviewing Chapter 12.

• Fixes wrongly used app reference to Fastify instance,
• Removes the command to expose port 3000 from microservices Dockerfile, as none of them listens to that port,
• Updates the 'main' key on package.json to be server.js instead of index.js,
• Removes white space and multiple empty lines at the end of files