DecisionTreeEncoder default value mismatch with Docs

[michaelrussell4]

Description

Very minor change. Just changing a default parameter value that was mistakenly set to 'raise' when it should have been 'ignore'.

The documentation states that for the DecisionTreeEncoder the default value for the unseen parameter is 'ignore' but this is inconsistent with the source code which has this default parameter set to 'raise', In order to be consistent with the documentation and the _docstrings/init_parameters/encoders.py _unseen_docstring value, the code should be updated to set this parameter to 'ignore' instead of 'raise'.

I noticed this error because I included the DecisionTreeEncoder in my pipeline and fitted the pipeline with my training data and then when I tried to work with test data, which included unseen values, this step raised an error, which is what it should do if unseen is set to 'raise' but not if it was set to what the documentation stated.

Screenshots