[Catalyst] Migrate Wi-Fi Hotspot preference

Bug: 368359963
Flag: com.android.settings.flags.catalyst_tether_settings
Test: Manual testing
atest -c TetherSettingsTest \
         TetherScreenTest

Change-Id: I89d418454af7887a4892c616f4efff481b536a91

tests/robotests/src/com/android/settings/network/tether/TetherScreenTest.kt

@@ -40,6 +40,9 @@ class TetherScreenTest : CatalystScreenTestCase() {
     override val flagName: String
         get() = Flags.FLAG_CATALYST_TETHER_SETTINGS
 
+    // TODO: Remove override (See b/368359963#comment7)
+    override fun migration() {}
+
     @Before
     fun setUp() {
         ShadowConnectivityManager.getShadow().setTetheringSupported(true)