Have separate tag for proxyv2 image

Similar to other locations in BB. I think it would be a good idea to separate the image tag from the registry name. This allows for easier upgrades when the time comes and separation of hub vs image. Also for consistency purposes.

This is the exact line that is in question: https://repo1.dso.mil/platform-one/big-bang/apps/core/istio-controlplane/-/blob/main/chart/values.yaml#L11

Example of the method that is found throughout BB is right in that same file at lines 5 and 8: https://repo1.dso.mil/platform-one/big-bang/apps/core/istio-controlplane/-/blob/main/chart/values.yaml#L5