Derive SUC service account name from configuration

We need to propagate the service account name of the System Upgrade Controller when creating upgrade plans, however, this is [currently hardcoded](https://github.com/suse-edge/upgrade-controller/blob/3ff187ef882fd1d6087d3102ef8b174274b5639b/internal/upgrade/base.go#L49). Investigate and find a solution to include it from a configuration option.