nixos/vector: add option to disable the configuration validation

Currently, during built time the configuration gets checked by vector.
This can be a problem if [environment
variables](https://vector.dev/docs/reference/environment_variables/) are
interpolated into the configuration. In this case the validation can be
disabled. This came up in trying to find a solution for
[#377889](https://github.com/NixOS/nixpkgs/issues/377889).

nixos/modules/services/logging/vector.nix

@@ -6,7 +6,6 @@
 }:
 let
   cfg = config.services.vector;
-
 in
 {
   options.services.vector = {
@@ -31,6 +30,14 @@ in
       '';
     };
 
+    validateConfig = lib.mkOption {
+      type = lib.types.bool;
+      default = true;
+      description = ''
+        Enable the checking of the vector config during build time. This should be disabled when interpolating environment variables.
+      '';
+    };
+
     settings = lib.mkOption {
       type = (pkgs.formats.json { }).type;
       default = { };
@@ -53,7 +60,7 @@ in
         let
           format = pkgs.formats.toml { };
           conf = format.generate "vector.toml" cfg.settings;
-          validateConfig =
+          validatedConfig =
             file:
             pkgs.runCommand "validate-vector-conf"
               {
@@ -65,7 +72,9 @@ in
               '';
         in
         {
-          ExecStart = "${lib.getExe cfg.package} --config ${validateConfig conf} --graceful-shutdown-limit-secs ${builtins.toString cfg.gracefulShutdownLimitSecs}";
+          ExecStart = "${lib.getExe cfg.package} --config ${
+            if cfg.validateConfig then (validatedConfig conf) else conf
+          }  --graceful-shutdown-limit-secs ${builtins.toString cfg.gracefulShutdownLimitSecs}";
           DynamicUser = true;
           Restart = "always";
           StateDirectory = "vector";