Docs mention `From` header is supported, but the lua doesn't read that header

https://ecosyste.ms/api says one way of accessing the polite pool is "Configure your [from request header](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/From).", but I don't see evidence in this repo that the `From` header is read

The issue identifies the ecosyste.ms API documentation and this Lua APISIX plugin, but no file or test. Start by tracing how request headers are handled in the plugin and compare that behavior with the documented `From` header. Done means the plugin behavior and API documentation agree, with the resulting behavior covered by a test if the repository has one.

Written by the indexing model from the issue text.