fix(tpl): ensure rough backward compat in `emqx_prometheus`

But also emit warning when job name template renders with errors.

apps/emqx_prometheus/src/emqx_prometheus.app.src

@@ -2,7 +2,7 @@
 {application, emqx_prometheus, [
     {description, "Prometheus for EMQX"},
     % strict semver, bump manually!
-    {vsn, "5.0.16"},
+    {vsn, "5.0.17"},
     {modules, []},
     {registered, [emqx_prometheus_sup]},
     {applications, [kernel, stdlib, prometheus, emqx, emqx_management]},

apps/emqx_prometheus/src/emqx_prometheus.erl

@@ -113,10 +113,18 @@ handle_info(_Msg, State) ->
 
 push_to_push_gateway(Uri, Headers, JobName) when is_list(Headers) ->
     [Name, Ip] = string:tokens(atom_to_list(node()), "@"),
-    JobName1 = emqx_connector_template:render_strict(
+    % NOTE: allowing errors here to keep rough backward compatibility
+    {JobName1, Errors} = emqx_connector_template:render(
         emqx_connector_template:parse(JobName),
         #{<<"name">> => Name, <<"host">> => Ip}
     ),
+    _ =
+        Errors == [] orelse
+            ?SLOG(warning, #{
+                msg => "prometheus_job_name_template_invalid",
+                errors => Errors,
+                template => JobName
+            }),
     Data = prometheus_text_format:format(),
     Url = lists:concat([Uri, "/metrics/job/", unicode:characters_to_list(JobName1)]),
     case httpc:request(post, {Url, Headers, "text/plain", Data}, ?HTTP_OPTIONS, []) of