WA wfc/eitc update

[yuantian0204]

Adjusting WA etic/wfc reduction parameters / variable code

Variable to amend: reduction rate

Parameter to amend: reduction rate

[yuantian0204]

We need to adjust the variable code to remove the out-dated hard-coded reduction rate; we can create new parameters for the production rate. Here is a summary of the WA wfc reduction rules https://docs.google.com/document/d/1lzz46uR-Atcj3oPWC870D6QfC9Hf_O96SeuDHPmkpSo/edit

We also need to update the parameters code to include more child count situations.

[yuantian0204]

@PavelMakarchuk

[MaxGhenis]

Please consult https://github.com/PolicyEngine/policyengine-us/discussions/1246

I don't recall the details but it explains why we implemented it as such originally