you can docker build & push, kubernetes deploy with this pipeline.
on gitlab project page
Infrastructure > Kubernetes > Connect cluster with agent
you can create new agent
type a name and create agent. after that click register
gitlab gave you token and helm command to install gitlab-agent
i recommend that giving cluster-admin permission for gitlab-agent so you can deploy easily with permission.
kubectl create clusterrolebinding gitlab-agent --clusterrole=cluster-admin --serviceaccount=gitlab-agent:gitlab-agent -n gitlab-agent
after installation and give permission you can use pipeline your kubernetes cluster.
kubectl config use-context "groupname/projectname:kubernetesconnectname"