feature: allow config of one release to be a function of another release's values

Consider erigon rpcdaemon: we would wish for proxyd config to react to that by pointing to the rpcdaemon service instead of erigon's. It may be true we could work around that by having the chart always create an SVC that points to the "right place" (an universal SVC, so to say)... but there is a general use-case here for having this capability.