fix(helm): Always respect configured registry in image references

Remove the dot-based heuristic that skipped prepending the registry
when the repository contained a dot. This caused explicitly configured
registries (both service-level and global) to be silently ignored for
repositories with dots in their path (e.g. mirror.gcr.io/grafana/loki).

Restores the pre-grafana#19347 behavior of always prepending the registry.

Fixes grafana#20663

Author: mag123c

production/helm/loki/templates/_helpers.tpl

@@ -163,8 +163,7 @@ Create the name of the service account to use
 
 {{/*
 Base template for building docker image reference
-Determines the final image name, respecting the global registry if defined, unless the local repository
-already contains a full registry (indicated by a dot '.') for backwards-compatibility.
+Always prepends the registry when one is configured (global or service-level).
 It also respects `.digest` as well as `.sha` (deprecated).
 */}}
 {{- define "loki.baseImage" }}
@@ -175,7 +174,7 @@ It also respects `.digest` as well as `.sha` (deprecated).
 {{- $ref := ternary (printf ":%s" (.service.tag | default .defaultVersion | toString)) ($digest) (empty $digest) -}}
 
 {{- $prefix := "" -}}
-{{- if and $registry (not (contains "." $repository)) -}}
+{{- if $registry -}}
 {{- $prefix = printf "%s/" $registry -}}
 {{- end -}}