Add PATCH support to our request lib modules

https://eaflood.atlassian.net/browse/WATER-3906
https://eaflood.atlassian.net/browse/WATER-3919

In order to call the [/generate](https://defra.github.io/sroc-charging-module-api-docs/#/bill-run/GenerateBillRun) bill run endpoint in the Charging Module API we need to be able to make `PATCH` http requests.

This change adds the functionality to `app/lib/request.lib.js` and `app/lib/charging-module-request.lib.js`.

Author: Cruikshanks