Backup NETWORK_AVOID_BAD_WIFI setting.

Add NETWORK_AVOID_BAD_WIFI to GlobalSettings allowlist and remove
from denylist in SettingsBackupTest.

Bug: 270097260
Test: atest SettingsBackupTest
Test: Manual test, confirm value restored after device reset and restore.
Change-Id: I1e0f41443bb12b7687e21e8b426c95b1a33b3fd9