convert sync endpoint to gn config

components/brave_sync/BUILD.gn

@@ -4,6 +4,20 @@ import("//tools/grit/grit_rule.gni")
 import("//tools/grit/repack.gni")
 import("buildflags/buildflags.gni")
 
+declare_args() {
+  brave_sync_endpoint = "https://sync-staging.brave.com"
+}
+
+if (is_official_build) {
+  brave_sync_endpoint = "https://sync.brave.com"
+}
+
+config("brave_sync_config") {
+  defines = [
+    "BRAVE_SYNC_ENDPOINT=\"$brave_sync_endpoint\""
+  ]
+}
+
 if (enable_brave_sync) {
   source_set("js_sync_lib_impl") {
     sources = [
@@ -18,6 +32,7 @@ if (enable_brave_sync) {
       "client/client_ext_impl_data.h",
     ]
 
+    configs += [ ":brave_sync_config" ]
     deps = [
       ":core",
       ":crypto",

components/brave_sync/brave_profile_sync_service_impl.cc

@@ -428,7 +428,7 @@ void BraveProfileSyncServiceImpl::OnGetInitData(
 
   client_data::Config config;
   config.api_version = brave_sync_prefs_->GetApiVersion();
-  config.server_url = "https://sync-staging.brave.com";
+  config.server_url = BRAVE_SYNC_ENDPOINT;
   config.debug = true;
   brave_sync_client_->SendGotInitData(seed, device_id, config, device_id_v2);
 }