github-runner docs: How to set base image

How to set base image

This charm supports deploying the runners on different base images.

By using juju config to change the charm configuration labels, the runner can be deployed with a different Ubuntu base image. Latest two LTS images “jammy” and “noble” are supported. The default base image is “jammy”.

juju config <APP_NAME> base-image=<BASE_IMAGE_TAG_OR_NAME>

An example of a BASE_IMAGE_TAG_OR_NAME value would be “jammy”, “22.04”, “noble”, “24.04”.