GitLab CI/CD template for ggshield

[ZGuardian]

Is your feature request related to a problem? Please describe.
Every time GitLab CI/CD users want to integrate ggshield in their CI workflows, they need to write their own GitLab CI .yaml file and configure the scanning. A CI/CD template (like GitHub Actions, CircleCI orbs) will lower the barriers to adoption/usage.

Describe the solution you'd like
This bolt-on template (similar to ggshield CircleCI orb) will help users integrate ggshield in their existing GitLab CI/CD workflow very easily. Here are a few examples from the GitLab CI/CD template registry.

GitLab provides a complete guide to developing CI/CD templates.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
GitGuardian is a GitLab Tech Alliance partner. Releasing a GitLab CI/CD template for ggshield will help further cement this partnership and provide developer marketing material to be used in the acquisition/growth campaigns.