Allow templating of registry hosts with `tpl`

Registry hosts (.Values.nexus.docker.registries) may contain the domain name inside of them which is not possible to parse from .Values.domain due to the $registry variable not being templated. See: https://repo1.dso.mil/platform-one/big-bang/apps/developer-tools/nexus/-/blob/main/chart/templates/bigbang/virtualservice.yaml#L47

Suggest (if possible) to template this using tpl as is done higher up in the same file with the Istio hosts: https://repo1.dso.mil/platform-one/big-bang/apps/developer-tools/nexus/-/blob/main/chart/templates/bigbang/virtualservice.yaml#L22