[feature] Ignore unreachable proof for services banned from a country

I'm in Indonesia right know where Reddit is not reachable.

Reddit proofs of all my contacts are then unreachable, and Keybase is spamming red all over the place, asking me to confirm that my contact are still legit one by one.

Of course I'm not willing to do that. But either way this is rather inconvenient and now I can't tell between actual broken proof or legit contacts anymore.

I think a way to tell Keybase Reddit that can't be reached and that this is not a big deal would be very helpful.

Start by locating the Keybase client logic that evaluates Reddit proofs and determines when an unreachable proof is reported. Define how a user would mark Reddit as unreachable and how that state should differ from a broken proof, then identify the tests needed to verify both cases.

Written by the indexing model from the issue text.