fix: bad prometheus schema for headers

apps/emqx_prometheus/src/emqx_prometheus.app.src

@@ -2,7 +2,7 @@
 {application, emqx_prometheus, [
     {description, "Prometheus for EMQX"},
     % strict semver, bump manually!
-    {vsn, "5.0.13"},
+    {vsn, "5.0.14"},
     {modules, []},
     {registered, [emqx_prometheus_sup]},
     {applications, [kernel, stdlib, prometheus, emqx, emqx_management]},

apps/emqx_prometheus/src/emqx_prometheus_api.erl

@@ -130,10 +130,8 @@ prometheus_data_schema() ->
         description =>
             <<"Get Prometheus Data. Note that support for JSON output is deprecated and will be removed in v5.2.">>,
         content =>
-            #{
-                'application/json' =>
-                    #{schema => #{type => object}},
-                'text/plain' =>
-                    #{schema => #{type => string}}
-            }
+            [
+                {'text/plain', #{schema => #{type => string}}},
+                {'application/json', #{schema => #{type => object}}}
+            ]
     }.

apps/emqx_prometheus/src/emqx_prometheus_schema.erl

@@ -59,7 +59,7 @@ fields("prometheus") ->
             ?HOCON(
                 list({string(), string()}),
                 #{
-                    default => [],
+                    default => #{},
                     required => false,
                     converter => fun ?MODULE:convert_headers/1,
                     desc => ?DESC(headers)