Updating visibility bit in the config string

Updating the InternalConfig::visibility field to a string instead of an
integer to make it compatible with the libassistant side changes.

Bug: b:143715504
Change-Id: I775a4b067ae0944733bd87ecc8869641006866cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1970807Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Commit-Queue: Abhijeet Singh <siabhijeet@google.com>
Cr-Commit-Position: refs/heads/master@{#727208}

chromeos/services/assistant/utils.cc

@@ -85,7 +85,7 @@ std::string CreateLibAssistantConfig(
 
   // Set DeviceProperties.visibility to Visibility::PRIVATE.
   // See //libassistant/shared/proto/device_properties.proto.
-  internal.SetKey("visibility", Value(1));
+  internal.SetKey("visibility", Value("PRIVATE"));
 
   if (base::SysInfo::IsRunningOnChromeOS()) {
     Value logging(Type::DICTIONARY);