Set retry in runner's config.toml

Description

Currently, the only way to have the runner retry a job is to set the retry keyword in the gitlab-ci.yml file. This is works if you want to set per-project runner retries, but it would be great to be able to set a retry amount directly in the config.toml Gitlab Runner file.

The use case is for a runner that supports many different projects, and occasionally has runner system failures, which we've been encountering with our Kubernetes runner. Currently to fix this we have to go at set retry keywords in every project and then maintain those across all of the projects.

Another possible solution is to be able to set default CI/CD parameters for an entire group.

Thanks!