Reduce duplication with Processor::API::Responder

@dkubb @mbj @solnic

I'm opening a PR for this because I wanted to get your input. Do you consider this a worthy change? It feels like reducing duplication like this, results in more complexity. Even though flog doesn't show an increase, I do consider the code added in `Processor::API::Responder` to be more complex than the previously present duplication. Also, flay count didn't decrease either.

I somewhat think that I still like the code in this PR more than the previous version, but I wanted to get your thoughts on a decision like this.

Thx!