Log usage of deault image for Docker and K8S executors

What does this MR do?

Adds logging of the usage of default image for Docker and Kubernetes executors.

Why was this MR needed?

Runner owners and maintainers, when they manage Docker/Kubernetes executors, need to define a default image that is used for the job if user don't specify it with image:.

While it's expected users will define an image that suits their jobs best (and probably more than 90% are doing that), some users may depend on the default image. Whether it's because they are new to GitLab CI/CD and not fully understand how it works or because the default image just works for them - their jobs may depend on what was present in the default image. Change of the default image, in that case, may potentially affect some of the workloads.

And runner maintainers usually need to update the default image from time to time. But for that, they may want to get a better understanding on how many of their users depend on the default image and how big impact such change could make.

This change provides this capability. Usage of the default image is logged together with the job id, and from here we can get into the repository URL which will allow to identify projects and namespaces that depend on it.

What's the best way to test this MR?

What are the relevant issue numbers?

Needed for gitlab-com/gl-infra/production-engineering#27011 (closed)