thunderbird: add extraConfig option

The added extraConfig option allowes users to insert custom text at
the end of the generated profile `user.js` file. This allows the users
to import templates as part of their configuration.

modules/programs/thunderbird.nix

@@ -94,12 +94,13 @@ let
       "mail.smtp.defaultserver" = "smtp_${id}";
     } // account.thunderbird.settings id;
 
-  mkUserJs = prefs: ''
+  mkUserJs = prefs: extraPrefs: ''
     // Generated by Home Manager.
 
     ${concatStrings (mapAttrsToList (name: value: ''
       user_pref("${name}", ${builtins.toJSON value});
     '') prefs)}
+    ${extraPrefs}
   '';
 in {
   meta.maintainers = with hm.maintainers; [ d-dervishi jkarlson ];
@@ -179,6 +180,14 @@ in {
                   *{scrollbar-width:none !important}
                 '';
               };
+
+              extraConfig = mkOption {
+                type = types.lines;
+                default = "";
+                description = ''
+                  Extra preferences to add to <filename>user.js</filename>.
+                '';
+              };
             };
           }));
       };
@@ -327,7 +336,8 @@ in {
           { "mail.openpgp.allow_external_gnupg" = profile.withExternalGnupg; }
 
           profile.settings
-        ] ++ (map (a: toThunderbirdAccount a profile) accounts)));
+        ] ++ (map (a: toThunderbirdAccount a profile) accounts)))
+          profile.extraConfig;
       };
     }));
   };

tests/modules/programs/thunderbird/thunderbird-expected-first.js

@@ -59,3 +59,5 @@ user_pref("mail.smtpserver.smtp_cda3f13b64c1db7d4b58ce07a31304a362d7dcaf14476bfa
 user_pref("mail.smtpservers", "smtp_bcd3ace52bed41febb6cdc2fb1303aebaa573e0d993872da503950901bb6c6fc,smtp_cda3f13b64c1db7d4b58ce07a31304a362d7dcaf14476bfabcca913ae41ada9f");
 user_pref("privacy.donottrackheader.enabled", true);
 
+user_pref("mail.html_compose", false);
+

tests/modules/programs/thunderbird/thunderbird-expected-second.js

@@ -29,3 +29,4 @@ user_pref("mail.smtpservers", "smtp_bcd3ace52bed41febb6cdc2fb1303aebaa573e0d9938
 user_pref("privacy.donottrackheader.enabled", true);
 user_pref("second.setting", "some-test-setting");
 
+

tests/modules/programs/thunderbird/thunderbird.nix

@@ -41,6 +41,9 @@
         userContent = ''
           * { color: red !important; }
         '';
+        extraConfig = ''
+          user_pref("mail.html_compose", false);
+        '';
       };
 
       second.settings = { "second.setting" = "some-test-setting"; };