[Feature] Overload policy with argparse

[bleetube]

This is a minor quality-of-life feature request asking for a command line parameters to make minor policy adjustments. e.g. charge-lnd --configure-policy mydefaults.min_fee_ppm_delta=250

For my use case, I currently maintain two almost identical config files. The only difference being min_fee_ppm_delta. My strategy is to run the script often-ish with a very high ppm delta. Then, once in a very long while, I will run it with the other config file to update fees with a lower ppm delta. This mostly limits channel fee updates to when the liquidity has significantly changed to more quickly incentivize (or not) routing, which is my way of balancing the trade off of failed forwards due to channel updates. If I could override this policy in my cronjob command, then I would only need to maintain a single configuration file.

Regardless of your response on this, thank you for writing this software. Before it existed I used to maintain a bash script that implemented my policies with clunky logic, and I would end up making routine manual changes. I have been running charge-lnd for years now and it rarely needs attention. Beautiful work.