The Toolhub chart includes mcrouter config adapted from work that @Joe did for the mediawiki chart. Part of this config is setting the tag version for the mcrouter and prometheus-mcrouter-exporter images used as sidecar containers.
Currently the helmfile.d settings for Toolhub contain explicit tags, but it would be more ideal for these to be shared configuration maintained for everyone in an /etc/helmfile-defaults file. This would follow the pattern already used for envoy sidecars.
One thing to work out would be the actual setting names. The Toolhub chart and the MediaWiki chart differ slightly in what values.yaml keys are expected to provide the values. The MediaWiki chart expects mw.mcrouter.{image_tag,exporter_version}. The Toolhub chart expects mcrouter.{image_tag,exporter_version} (no mw parent).