[Minor] Refer to third parties for attachment handling whenever possible

This avoids confusion and enqueries to the rspamd project, if it is made
clear that the decision to score certain attachments high has been
incorporated from a well-known third party, such as Google's or
Microsoft's attachment handling policy.

src/plugins/lua/mime_types.lua

@@ -52,16 +52,10 @@ local settings = {
   },
 
   bad_extensions = {
-    bat = 2,
-    chm = 4,
-    com = 2,
     cue = 2,
     exe = 1,
-    hta = 2,
     iso = 4,
     jar = 2,
-    lnk = 4,
-    scr = 4,
     -- In contrast to HTML MIME parts, dedicated HTML attachments are considered harmful
     htm = 1,
     html = 1,
@@ -105,7 +99,10 @@ local settings = {
     app = 4,
     asp = 4,
     bas = 4,
+    bat = 4,
+    chm = 4,
     cnt = 4,
+    com = 4,
     csh = 4,
     diagcab = 4,
     fxp = 4,
@@ -113,9 +110,11 @@ local settings = {
     grp = 4,
     hlp = 4,
     hpj = 4,
+    hta = 4,
     inf = 4,
     its = 4,
     jnlp = 4,
+    lnk = 4,
     ksh = 4,
     mad = 4,
     maf = 4,
@@ -160,6 +159,7 @@ local settings = {
     pst = 4,
     reg = 4,
     scf = 4,
+    scr = 4,
     shs = 4,
     theme = 4,
     url = 4,