[CHORE] flake8 issues E402, E721 and F821 (#1874)

* F821: undefine name
disabled and logged webhook_listener for opennode and lnpay because they are obviously not working
* E402: module level import not at top of file
* E721 fixes, only popped up for python3.9 not 3.10

lnbits/core/views/api.py

@@ -468,7 +468,7 @@ async def api_payments_sse(
 async def api_payment(payment_hash, X_Api_Key: Optional[str] = Header(None)):
     # We use X_Api_Key here because we want this call to work with and without keys
     # If a valid key is given, we also return the field "details", otherwise not
-    wallet = await get_wallet_for_key(X_Api_Key) if type(X_Api_Key) == str else None  # type: ignore
+    wallet = await get_wallet_for_key(X_Api_Key) if isinstance(X_Api_Key, str) else None  # type: ignore
 
     # we have to specify the wallet id here, because postgres and sqlite return internal payments in different order
     # and get_standalone_payment otherwise just fetches the first one, causing unpredictable results