Automate project onboarding of public projects using Terraform

This change automates the manual processes to onboard a new project to the renovate bot.

This is a PoC and up for discussion.

I would like to know if this is something you think is valuable.

A few things that would need to be done:

• Clarify if it is okay that the Terraform code "imports" projects instead of "forking" them.
• Complete the projects/config.tfvars list of projects
• Import the existing forks into the Terraform state
• Make sure it works for all existing cases :D
• Add a GITLAB_TOKEN of the bot user to the CI/CD variables
• Properly integrate with the pipeline schedules and the currently manual terraform:apply job.

This would also help the GitLab Terraform Provider in terms of dogfooding 💃