feat: add generic lnurl error response handler (#2638)

* feat: add generic lnurl error response handler

this is used multiple times in extensions to safeguard `views_lnurl.py`
endpoint to not return a wrong lnurl error response.

you use it by just setting following on your lnurl router/view

```
withdraw_ext_lnurl = APIRouter(prefix="/api/v1/lnurl")
withdraw_ext_lnurl.route_class = LNURLErrorResponseHandler
```

lnbits/core/services.py

@@ -25,6 +25,7 @@ from lnbits.decorators import (
     check_user_extension_access,
     require_admin_key,
 )
+from lnbits.exceptions import InvoiceError, PaymentError
 from lnbits.helpers import url_for
 from lnbits.lnurl import LnurlErrorResponse
 from lnbits.lnurl import decode as decode_lnurl
@@ -70,18 +71,6 @@ from .helpers import to_valid_user_id
 from .models import BalanceDelta, Payment, PaymentState, User, UserConfig, Wallet
 
 
-class PaymentError(Exception):
-    def __init__(self, message: str, status: str = "pending"):
-        self.message = message
-        self.status = status
-
-
-class InvoiceError(Exception):
-    def __init__(self, message: str, status: str = "pending"):
-        self.message = message
-        self.status = status
-
-
 async def calculate_fiat_amounts(
     amount: float,
     wallet_id: str,