chameleon: Add support for advertising with a RPA

This change enhances Bluetooth LE advertising by adding support for RPA
on Chameleond.

The following features are implemented:
  1. A `privacy` option is added to the security in config, allowing
     advertising with a random address to be enabled or disabled.
  2. A `GetRandomAddress` gRPC method is added to retrieve the current
     RPA being used by Chameleond.

BUG=b:389553215
TEST=Bluetooth HID test

Change-Id: I8bb2a845d982aac180c2954962b57e2495d18d50
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/chameleon/+/7274988
Reviewed-by: Hsin-chen Chuang <chharry@google.com>
Commit-Queue: Michael Sun <michaelfsun@google.com>
Reviewed-by: Yun-hao Chung <howardchung@chromium.org>
Tested-by: Yulun Liu <yulun@google.com>