nixos/matrix-synapse: expose rendered config file as readOnly option

nixos/modules/services/misc/matrix-synapse.nix

@@ -122,6 +122,14 @@ in {
   options = {
     services.matrix-synapse = {
       enable = mkEnableOption "matrix.org synapse";
+      configFile = mkOption {
+        type = types.str;
+        readOnly = true;
+        description = ''
+          Path to the configuration file on the target system. Useful to configure e.g. workers
+          that also need this.
+        '';
+      };
       package = mkOption {
         type = types.package;
         default = pkgs.matrix-synapse;
@@ -706,6 +714,8 @@ in {
       }
     ];
 
+    services.matrix-synapse.configFile = "${configFile}";
+
     users.users.matrix-synapse = {
       group = "matrix-synapse";
       home = cfg.dataDir;