update secret name in kubevirt-manager-certificate

Summary

kubevirt-manager-certificate Certificate was specifying a wrong secret name (keycloak-tls) resulting in kubevirt-manager Ingress to refer to a non-existing Secret.

The naming convention defined in kustomize-units/tls-components/tls-certificate should apply:

certificate name: kubevirt-manager-certificate secret name: kubevirt-manager-tls

related references

https://gitlab.com/sylva-projects/sylva-core/-/blob/82f49a37903d3d124e11592ed567130260902d0c/kustomize-units/kubevirt-manager/kubevirt-manager-certificate.yaml#L20

Closes #1854 (closed)