Add docker example for the async sample app

[samuel-holt]

Overview

Add docker support for the async sample app. The app will run on port 8888 by default.

Updates

• Add Dockerfile and docker-compose.yml
• Fix some formatting issues in the sample app

[izsi-salmon]

Just added a note from when I set up the sample app locally using docker.

[izsi-salmon]

I think we might need to add an extra step here to do docker-compose build first. In my experience I had an error when opening the browser because Docker couldn't find the vendor autoload script needed to load raygun4php dependencies. This was because I installed the dependencies outside of the src folder before setting up Docker. I added them to src but continued to get a not found error until I tried building.

Probably a pretty obvious step but it did get me stuck 😅 would be good to include it, as you need to run docker-compose build every time you make changes before running docker-compose up to see the changes.

[izsi-salmon]

I found out you can do this in one line by running it with the build option: docker-compose up --build