Add required tools for documentation build to devcontainer

[mgajek-cern]

Description:

To streamline the development setup and ensure consistency, we should install all necessary tools for building the documentation inside the devcontainer.

Missing tools to install:

• mdl ([markdownlint](https://github.com/markdownlint/markdownlint))

  gem install mdl

Additional steps:

• Install Python dependencies from tools/requirements.txt using:

  python3 -m pip install -r tools/requirements.txt

• Install website dependencies by running:

  (cd website && yarn install)

Goal:
Developers should have a ready-to-go environment with all prerequisites installed inside the devcontainer for documentation development and testing.