Document adding a job to GitLab CICD

[Bengt]

This documents how to add a job to GitLab CI/CD for running Bandit.

[lukehinds]

Thanks! Good addition. Looking at this though, makes me realise we should really start producing our own images, just in case cytopia/bandit:1-py3.10 were to fall into bad hands. I will raise an issue, but until then let's keep this PR open.

[Bengt]

Hello, @lukehinds! Thanks for considering this contribution. Yes, I also noticed that using the cytopia image is suboptimal and first-party Docker images would be preferable. By adding this job to the documentation, users might get encouraged to trust the source of the image. I have subscribed to the issue about creating such an image, so I can update this PR with the image name.

[lukehinds]

We now have official images: https://github.com/PyCQA/bandit?tab=readme-ov-file#container-images

[ericwb]

I think it would be better to start a new integrations doc. There are a slew of various ways Bandit can be integrated into various systems, Jenkins, Flake8, Ruff, VSCode, Vim, Emacs, Sonarqube, GitHub Action, pre-commit, etc, etc