Add known policy parameter values for 2024

[martinholmer]

Add 2024 values for inflation-indexed policy parameters in policy_current_law.json.

Do this by updating the update_pcl.py script (introduced by PR #2806) rather than by hand.

As mentioned in issue #2805, hand updating of policy_current_law.json is tedious and error-prone because the ParamTools-required layout of the json file means that the all the values for a given year of a vector parameter cannot all be seen in one editor window.