feat: filter response fields for /api/v1/payments/decode (#2612)

* feat: filter response fields

* chore: `make format`

* chore: comment

* Update lnbits/helpers.py

Co-authored-by: Pavol Rusnak <pavol@rusnak.io>

* Update lnbits/helpers.py

Co-authored-by: Pavol Rusnak <pavol@rusnak.io>

* chore: code format

---------

Co-authored-by: Pavol Rusnak <pavol@rusnak.io>

lnbits/helpers.py

@@ -223,3 +223,10 @@ def decrypt_internal_message(m: Optional[str] = None) -> Optional[str]:
     if not m:
         return None
     return AESCipher(key=settings.auth_secret_key).decrypt(m)
+
+
+def filter_dict_keys(data: dict, filter_keys: Optional[list[str]]) -> dict:
+    if not filter_keys:
+        # return shallow clone of the dict even if there are no filters
+        return {**data}
+    return {key: data[key] for key in filter_keys if key in data}