fix(lndrest): use boolean for allow_self_payment instead of integer

LND's /v2/router/send endpoint expects allow_self_payment to be a JSON
boolean, not an integer. Sending 1 instead of true causes a 400 error:
'proto: invalid value for bool type: 1'

Fixes payments failing when lnd_rest_allow_self_payment is enabled.

lnbits/wallets/lndrest.py

@@ -178,7 +178,7 @@ class LndRestWallet(Wallet):
             "no_inflight_updates": True,
         }
         if settings.lnd_rest_allow_self_payment:
-            req["allow_self_payment"] = 1
+            req["allow_self_payment"] = True
 
         try:
             r = await self.client.post(