feat(django-apps): allow adding extra init steps

modules/nixos/django-apps/default.nix

@@ -445,6 +445,15 @@ in
               doBackups = mkEnableOption "backups for this site" // {
                 default = true;
               };
+
+              extraInit = mkOption {
+                type = lines;
+                description = ''
+                  Steps taken during the initialization after the migration is done
+                  and the static files have been collected.
+                '';
+                default = '''';
+              };
             };
           }
         )
@@ -722,18 +731,24 @@ in
               inherit after environment path;
 
               preStart = ''
+                # Create the necessary directory with the correct user/group
+                mkdir -p ${config.mediaDirectory} ${config.staticDirectory}
+
                 if [ ! -f .initialized ]; then
                   # The previous initialization might have failed, so restart from the beginning
                   rm -rf source
 
                   # We need to download the application source and run the migrations first
                   ${lib.getExe pkgs.git} clone --single-branch --branch ${config.branch} ${config.source} source
-                  (cd source && python ${config.managePath} migrate --no-input && python ${config.managePath} collectstatic --no-input)
+                  pushd source
+                  python ${config.managePath} migrate --no-input
+                  python ${config.managePath} collectstatic --no-input
+
+                  ${config.extraInit}
+
+                  popd
                   touch .initialized
                 fi
-
-                # Create the necessary directory with the correct user/group
-                mkdir -p ${config.mediaDirectory} ${config.staticDirectory}
               '';
 
               requires = optional (config.application.type != "daphne") "dj-${name}.socket";