Support default imagePullSecrets in runner pod for private docker registries

[fgalind1]

Is your feature request related to a problem?.
When using a private docker registry it is required to provide the docker image as a imagePullSecrets in the runner pod spec. Runner pod spec supports imagePullSecrets, however it's quite useful to support this at the controller level with a default value similarly as it's done for runner image

Describe the solution you'd like
In the same way as a cmdline argument is supported to provide --runner-image, I'd like to have an option --runner-image-pull-secret-name or something similar that contains the secret name that holds the docker config and then use that to add the imagePullSecrets in the runner pod with something like:

	if defaultRunnerImagePullSecretName != "" {
		pod.Spec.ImagePullSecrets = []corev1.LocalObjectReference{
			{Name: defaultRunnerImagePullSecretName},
		}
	}

Describe alternatives you've considered
Define the imagePullSecrets for every single RunnerDeployment which could be repetitive and prune to errors

Additional context
N/A

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[fgalind1]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

waiting for review of PR #921