Add configurable captive portal probes

The probes allow testing for a configurable status code and location
header (regexes). They are disabled by default, so this CL is a
no-op unless the probe configurations are pushed.

Bug: b/79499239
Test: tests in CL pass, manual: captive portal login works
Change-Id: I785723aaed06054b9aa8ebff77803f23d7836db9
diff --git a/core/tests/coretests/src/android/provider/SettingsBackupTest.java b/core/tests/coretests/src/android/provider/SettingsBackupTest.java
index 5b7fc6e..14cf0a3 100644
--- a/core/tests/coretests/src/android/provider/SettingsBackupTest.java
+++ b/core/tests/coretests/src/android/provider/SettingsBackupTest.java
@@ -155,6 +155,7 @@
                     Settings.Global.CAPTIVE_PORTAL_HTTP_URL,
                     Settings.Global.CAPTIVE_PORTAL_MODE,
                     Settings.Global.CAPTIVE_PORTAL_OTHER_FALLBACK_URLS,
+                    Settings.Global.CAPTIVE_PORTAL_FALLBACK_PROBE_SPECS,
                     Settings.Global.CAPTIVE_PORTAL_SERVER,
                     Settings.Global.CAPTIVE_PORTAL_USE_HTTPS,
                     Settings.Global.CAPTIVE_PORTAL_USER_AGENT,