convert element tree json -> html (#299)

skyvern/exceptions.py

@@ -217,3 +217,8 @@ class BitwardenTOTPError(BitwardenBaseError):
 class BitwardenLogoutError(BitwardenBaseError):
     def __init__(self, message: str) -> None:
         super().__init__(f"Error logging out of Bitwarden: {message}")
+
+
+class UnknownElementTreeFormat(SkyvernException):
+    def __init__(self, fmt: str) -> None:
+        super().__init__(f"Unknown element tree format {fmt}")