Ensure Internal entity exceptions are correctly handled

As discussed here: https://github.com/Azure/azure-functions-durable-python/pull/184

There's an outstanding discussion about what to do when an entity errors out due to an internal exception. For example: what if an operation is missing its name.

One possibility is to propagate the error back to the orchestrator, same as if it were a user-code-level exception. Another approach is to error out completely and let the extension handle it, which is our current approach.