fix: problems reported by dialyzer

apps/emqx/include/emqx_trace.hrl

@@ -33,7 +33,7 @@
     extra = #{} :: map() | '_',
     start_at :: integer() | undefined | '_',
     end_at :: integer() | undefined | '_',
-    formatter = plain :: plain | json
+    formatter = plain :: plain | json | '_'
 }).
 
 -define(SHARD, ?COMMON_SHARD).

apps/emqx/src/emqx_trace/emqx_trace_handler.erl

@@ -46,7 +46,8 @@
     name := binary(),
     type := clientid | topic | ip_address,
     filter := emqx_types:clientid() | emqx_types:topic() | emqx_trace:ip_address(),
-    payload_encode := text | hidden | hex
+    payload_encode := text | hidden | hex,
+    formatter => json | plain
 }.
 
 -define(CONFIG(_LogFile_), #{