Enable kSystemBluetoothAdapterEnabled to be toggled by settingsPrivate

It was not possible to change the login screen profile's default
bluetooth preference through settingsPrivate. This cl enables that
behavior.

Bug: b:161902990
Change-Id: Ib0f0f798994182a19ee01562d7d5899667b58525
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2500445Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Commit-Queue: Billy Zhao <billyzhao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821759}

chrome/browser/extensions/api/settings_private/prefs_util.cc

@@ -571,6 +571,8 @@ const PrefsUtil::TypedPrefMap& PrefsUtil::GetAllowlistedKeys() {
       settings_api::PrefType::PREF_TYPE_BOOLEAN;
   (*s_allowlist)[::ash::prefs::kUserBluetoothAdapterEnabled] =
       settings_api::PrefType::PREF_TYPE_BOOLEAN;
+  (*s_allowlist)[::ash::prefs::kSystemBluetoothAdapterEnabled] =
+      settings_api::PrefType::PREF_TYPE_BOOLEAN;
   (*s_allowlist)[::ash::prefs::kVpnConfigAllowed] =
       settings_api::PrefType::PREF_TYPE_BOOLEAN;
   (*s_allowlist)[arc::prefs::kAlwaysOnVpnPackage] =