Resolve "degree" parameter for STLDecomposer

In https://github.com/alteryx/evalml/pull/3741 we created the `STLDecomposer` component. Like the `PolynomialDecomposer` it has a parameter for `degree`. This parameter makes sense for the PolynomialDecomposer, but is more ambiguous when it comes to the STLDecomposer. [statsmodels STL tutorial](https://www.statsmodels.org/dev/examples/notebooks/generated/stl_decomposition.html) in the statsmodels [STL source code](https://github.com/statsmodels/statsmodels/blob/main/statsmodels/tsa/stl/_stl.pyx), we see that there are 3 "degree" parameters for STL that can be adjusted, all related to the LOESS smoothing. We need to decide how we want to use degree to perhaps access these values. One possible way is to pass in a dictionary.