Add DevContainer configuration and add `.idea` folder to gitignore

[AFCMS]

How to test?

Try the integration with any supported editors.

With VSCode:

• Install VSCode
• Install and enable Dev Containers support: https://marketplace.visualstudio.com/items?itemName=ms-vscode-remote.remote-containers
• Open the cloned repository in VSCode
• Notice the popup telling you about the presence of the dev container config file
• Click the reload editor button on the popup
• Wait until it downloads the base image and the VSCode server
• Open an integrated terminal (should be the container shell, not the host shell)
• Try to run bundle exec jekyll serve
• Notice the popup in VSCode asking you of opening the container served port in the browser