HillasIntersection with weighting = "hess" does not work

[calispac]

Describe the bug
The weighting method 'hess' of the HillasIntersection reconstructor is not implemented although it is listed as a possible method.

To Reproduce

HillasIntersection(subarray=example_subarray, weighting='hess')

Expected behavior
As weighting = 'hess' is listed in the allowed values of the HillasIntersection I would except this to work.
See :

ctapipe/src/ctapipe/reco/hillas_intersection.py

Line 92 in 26ded3f

weighting = traits.CaselessStrEnum(

Supporting information
Here is the error
AttributeError: 'HillasIntersection' object has no attribute '_weight_method

Additional context
This error is simply due to the fact that 'hess' method is not implemented in the class. I suggest to either

1. to implement weighting = 'hess' if someone has a ref.
2. to remove weighting = 'hess' from the possible listed methods.
3. to raise a NotImplementedError when weighting = 'hess' is used

I would also suggest to add a weighting='equal' method to make the intersection without weights (for benchmark with other methods).