Add renovate bot

What does this merge request do and why?

Follow the steps laid out in https://gitlab.com/gitlab-com/gl-infra/common-ci-tasks/-/blob/main/renovate-bot.md to enable dependency update with Renovate.

1. Ensure that a validate and renovate_bot stages exists in your .gitlab-ci.yml configuration
2. Create a Project Access Token with api and write_repository scope and make it available in your CI environment via the RENOVATE_GITLAB_TOKEN environment variable through the CI/CD Variables settings. Make sure the variable is Protected and Masked.
3. Lookup the GitHub Personal Access token from 1Password Production Vault and save it into the CI environment variable RENOVATE_GITHUB_TOKEN. Make sure the variable is Protected and Masked. - I can't find this 🤔.
4. Note that you can use Group Access Tokens and Group CI/CD variables, instead of Project-level ones should you choose.
5. Create a CI Pipeline Schedule called Renovatebot with a daily schedule, eg 0 1 * * *. Ensure that the CI Pipeline schedule includes a variable, RENOVATE_SCHEDULED with a value of 1.
6. Note that Renovate Bot will only run on gitlab.com. For projects that are mirrored to other GitLab instances, the task will not run.
7. Create a renovate.json file in the root of the project.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.

Closes #238 (closed)