Migrate some gke-devops-general jobs to product runners if possible.

The gke-devops-general runner can sometimes get overloaded when a number of pipelines kick off. While we have to have gke-devops-general available for products without dedicated runners, we do have dedicated runners for some products.

• Add a CI variable to the uis/devops group: GENERAL_RUNNER_TAG with value gke-devops-general.
• Replace all the hardcoded tags: [gke-devops-general] in our templates with tags: [${GENERAL_RUNNER_TAG}].
• Teach the gitlab runner infrastructure project to additionally set the GENERAL_RUNNER_TAG variable for projects/groups which have dedicated runners available.