Rename `ClusterPlatformConfigureWorker` to `ClusterConfigureWorker`
This is a follow up of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22308.
After https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22308, we'll have two workers that call Clusters::RefreshService
to create missing kubernetes namespaces for specific Cluster or for clusters in a Projects:
I'd vouch to rename ClusterPlatformConfigureWorker
to simply ClusterConfigureWorker