This is a Community Wiki answer partially based on other user's comments, so feel free to edit it and add any additional details you consider important.

As you can read in this section of the official kubernetes documentation, it can be configured on a container runtime level ( in this case Docker ) by creating a Secret based on existing Docker credentials and later you can refer to such alternative cofiguration in your Pod specification as follows:

apiVersion: v1
kind: Pod
metadata:
  name: private-reg
spec:
  containers:
  - name: private-reg-container
    image: <your-private-image>
  imagePullSecrets: 👈
  - name: regcred