Add safe and well maintained operator for running external code from web sources

prototype:
```python 
class WebModuleOperator(FieldOperator):
    source_urls: List[str] # all downloaded to tempdir
    function: str # imported from tempdir when set
    hash: str # used to make sure the files hasnt changed

    def prepare(self):
        # here come your logic to set things up

    def process(self, value):
        return self._loaded_func(value)
```