feat(devcontainer): add devcontainer settings for dev environment

FROM php:latest

RUN apt-get update && apt-get install -y \

    libicu-dev \

    && docker-php-ext-install intl

COPY --from=composer /usr/bin/composer /usr/bin/composer

RUN apt-get update && \

    apt-get upgrade -y && \

    apt-get install -y git

// For format details, see https://aka.ms/vscode-remote/devcontainer.json or this file's README at:

// https://github.com/microsoft/vscode-dev-containers/tree/v0.117.1/containers/docker-existing-dockerfile

{

	"name": "Existing Dockerfile",

	"dockerFile": "./Dockerfile",

	"settings": {

		"terminal.integrated.shell.linux": null

	},

	"extensions": [

		"mikestead.dotenv",

		"bmewburn.vscode-intelephense-client",

		"streetsidesoftware.code-spell-checker",

		"naumovs.color-highlight",

		"heybourn.headwind"

	]

}

 No newline at end of file

```

Check [docker](https://docs.docker.com/engine/reference/commandline/docker/) and [docker-compose](https://docs.docker.com/compose/reference/) documentations for more insights.

### Developing inside a Container

If you're working in VSCode, you can take advantage of the `./.devcontainer/` folder. It defines a development container with preinstalled VSCode extensions so you don't have to worry about them. The container will be loaded with php, composer and git:

1. Install the VSCode extension [Remote - Containers](https://marketplace.visualstudio.com/items?itemName=ms-vscode-remote.remote-containers)

2. `Ctrl/Cmd + Shift + P` > `Open in container`

The VSCode window will reload inside the dev container.

You can check that the required packages are running in the console (`Terminal` > `New Terminal`):

```bash

php -v

composer -V

git version

```

For more info, see [VSCode Remote Containers](https://code.visualstudio.com/docs/remote/containers)