[Thread] add missing permissions to ThreadNetworkDemoApp

The privileged permissions needs to be included in the allowlist to be
able to pre-install the ThreadNetworkDemoApp.

Otherwise RuntimeException like below will be thrown to stop the device
from booting up:

```
03-18 07:13:46.288  4920  4920 E AndroidRuntime: java.lang.IllegalStateException: Signature|privileged permissions not in privileged permission allowlist:
```

Bug: 330097284
Test: `lunch aosp_cf_x86_64_phone-trunk_staging-userdebug && m` and
verified that the demoapp can be started

Change-Id: Ia6876e2eff1cde837be9e69954b2c749525e9e3c
2 files changed