[Minor] Unify configuration file structure

conf/scores.d/headers_group.conf

 # See https://rspamd.com/doc/tutorials/writing_rules.html for details
 
 description = "Various headers checks";
+
 max_score = 8.0;
 
 symbols = {

conf/scores.d/mime_types_group.conf

 # See https://rspamd.com/doc/tutorials/writing_rules.html for details
 
 description = "Mime attachments rules";
-# Define some limit for this group
-max_score = 10.0;
 
+max_score = 10.0;
 
 symbols = {
     "MIME_GOOD" {
         description = "Filename with known obscured unicode characters";
         one_shot = true;
     }
-}
+}

conf/scores.d/subject_group.conf

 
 description = "Subject filters";
 
+max_score = 6.0;
+
 symbols = {
 }
-
-max_score = 6.0;