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
Merged-In: Iec7a74bbf2569a91e958c497200d77e8451cbf7b
Merged-In: Ia958815325d1466345e9626efc8f62fc9d08d774
(clean cherry-pick of pi-dev I785723aaed06054b9aa8ebff77803f23d7836db9)

Change-Id: I18b3f263fed08fa4fee20d5e88f3ec8647d7f835