feat: Unconditionally produce debug comments

Rationale for eliminating the check to see if the `DEBUG` environment
variable holds a true value:
  * The `DEBUG` environment variable might be set on a container (for
    purposes specific to that container, not `nginx-proxy`) to a value
    that cannot be parsed as a bool, which would break `nginx-proxy`.
  * It simplifies the template.
  * It eliminates a cold code path.
  * It avoids heisenbugs.
  * It makes debugging easier for users.

Also delete the debug info tests, as they are fragile and they provide
limited value.

Alternatively, we could avoid collision with the container's use of
the `DEBUG` environment variable by using a container label [1] such
as `com.google.nginx-proxy.nginx-proxy.debug`.  I think doing so has
dubious value, especially if we want to attempt backwards
compatibility with the `DEBUG` environment variable.

Fixes #2139

[1] https://docs.docker.com/engine/reference/commandline/run/#-set-metadata-on-container--l---label---label-file

Co-authored-by: Nicolas Duchon <nicolas.duchon@gmail.com>

nginx.tmpl

@@ -12,7 +12,6 @@
 {{- $_ := set $globals "nginx_proxy_version" (coalesce $globals.Env.NGINX_PROXY_VERSION "") }}
 {{- $_ := set $globals "external_http_port" (coalesce $globals.Env.HTTP_PORT "80") }}
 {{- $_ := set $globals "external_https_port" (coalesce $globals.Env.HTTPS_PORT "443") }}
-{{- $_ := set $globals "debug_all" $globals.Env.DEBUG }}
 {{- $_ := set $globals "sha1_upstream_name" (parseBool (coalesce $globals.Env.SHA1_UPSTREAM_NAME "false")) }}
 {{- $_ := set $globals "default_root_response" (coalesce $globals.Env.DEFAULT_ROOT "404") }}
 {{- $_ := set $globals "trust_downstream_proxy" (parseBool (coalesce $globals.Env.TRUST_DOWNSTREAM_PROXY "true")) }}
@@ -106,22 +105,18 @@
 
 {{- define "upstream" }}
     {{- $networks := .Networks }}
-    {{- $debug_all := .Debug }}
 upstream {{ .Upstream }} {
     {{- $server_found := false }}
     {{- range $container := .Containers }}
-        {{- $debug := parseBool (coalesce $container.Env.DEBUG $debug_all "false") }}
         {{- /* If only 1 port exposed, use that as a default, else 80 */}}
         {{- $defaultPort := (when (eq (len $container.Addresses) 1) (first $container.Addresses) (dict "Port" "80")).Port }}
         {{- $port := (coalesce $container.Env.VIRTUAL_PORT $defaultPort) }}
         {{- $address := where $container.Addresses "Port" $port | first }}
-        {{- if $debug }}
     # Exposed ports: {{ $container.Addresses }}
     # Default virtual port: {{ $defaultPort }}
     # VIRTUAL_PORT: {{ $container.Env.VIRTUAL_PORT }}
-            {{- if not $address }}
+        {{- if not $address }}
     # /!\ Virtual port not exposed
-            {{- end }}
         {{- end }}
         {{- range $knownNetwork := $networks }}
             {{- range $containerNetwork := sortObjectsByKeysAsc $container.Networks "Name" }}
@@ -292,7 +287,7 @@ server {
             {{- $upstream = printf "%s-%s" $upstream $sum }}
         {{- end }}
 # {{ $host }}{{ $path }}
-{{ template "upstream" (dict "Upstream" $upstream "Containers" $containers "Networks" $globals.CurrentContainer.Networks "Debug" $globals.debug_all) }}
+{{ template "upstream" (dict "Upstream" $upstream "Containers" $containers "Networks" $globals.CurrentContainer.Networks) }}
     {{- end }}
 
     {{- $default_host := or ($globals.Env.DEFAULT_HOST) "" }}