Handle interception probing payments

probing payments uses a probing payment hash which is:
sha256("probing-01:" || payment_hash).

When the interceptor detects such a hash for a payment which is supposed
to trigger a channel creation , it checks if the destination is online,
and if online, fails with INCORRECT_OR_UNKNOWN_PAYMENT_DETAILS error in
order to let the payer knows that the payment would be successful.

postgresql/migrations/000004_create_probe_payments_hash_index.down.sql

@@ -0,0 +1 @@
+DROP INDEX probe_payment_hash;

postgresql/migrations/000004_create_probe_payments_hash_index.up.sql

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+CREATE INDEX probe_payment_hash ON public.payments (sha256('probing-01:' || payment_hash));