Effect of imagePullPolicy on peerd behavior and performance

For the community to adopt peerd, we need clarification on what happens for each of the `imagePullPolicy` configurations for a workload. For example, what is not clear to me is if `imagePullPolicy == always`, does it resolve to (1) pulling from the upstream registry or (2) pulling from fellow peers first because peerd is configured as a containerd mirror. Having this explicitly clarified would help community adoption.

For this work item to be closed, we need:
* An architecture diagram showing the paths for each imagePullPolicy configuration and its effect on peerd (whether the image is already present on the node vs not)