Python Operator

[dominiklohmann]

To make prototyping easier, we want to add a python operator that allows for modifying events one at a time. We are aiming at a syntax like this:

python '
  foo = x * y
  bar = sqrt(foo)
'

Which given the input {"x": 2, "y": 8} should result in {"x": 2, "y": 8, "foo": 16, "bar": 4}. This is an enabler for the Dashboard Page for which we are likely to need more flexible data transformations than TQL currently allows.

### Definition of Done
- [x] Agree on the desired semantics and syntax
- [x] Implement the operator
- [x] Write documentation

[tobim]

Blog post idea: Use pywhois to retrieve the AS Names of public IP addresses.