Floss: Add --log-output to btadapterd

Similar to btmanagerd, this adds `--log-output` to select whether
syslog or stderr is used for Rust's log output.

Also forwards GD debug flag if `--debug` is given.

Bug: 228905413
Tag: #floss
Test: Manual - Run btadapterd on Linux

Change-Id: I56cf3cb684b62ec2fdb5bdb50cf66abdaaf014fc