GitLab label change - workflow:customer-review -> workflow:needs-verification

We have made a slight change to the labels used to indicate an issue’s state on GitLab for ParaView to make its meaning clearer.

After an issue has been resolved to the satisfaction of ParaView developers, please mark issues as workflow:needs-verification instead of workflow:customer-review. The new tag serves the same purpose, which is to indicate the issue is ready for verification by an outside reviewer to sign off on (most often @wascott).