add ot-cli-ftd in /system/bin/ for eng and userdebug builds

`ot-cli-ftd` is a CLI tool simulating a node in Thread network. See https://www.threadgroup.org/ about Thread networking technology.

It's currently in `/vendor/bin/` but we're moving it to `/system/bin/` because `ot-cli-ftd` will be used in various CI tests.

`ot-cli-ftd` is also useful for debugging purpose.

Bug: 309051262
Test: Verified on Cuttlefish.

Change-Id: I96bf2bd7575540dc86e969a80cd9bb5634c3a1ea