Provide Scorers with the @k parameter from Settings

[david-fisher]

Is your feature request related to a problem? Please describe.
As a relevance engineer, I would like to evaluate my cases at a number of different values of k for any given metric. To do so, I currently need to define a new custom scorer for each value of k.

Describe the solution you'd like
Using either the Number of Results to Show value as k, or specifying a separate parameter, k, pass that value in the the scorers in the same fashion as qoption is passed in for individual queries.

This would allow implementing a single scorer for a metric, eg:

RR@k

const k = get_k()
let rank = 0;
eachDoc(function(doc, i) {
    if (rank === 0 && hasDocRating(i) && (docRating(i)) > 1) { // Make binary 0,1 are irrelevant, 2 and above is relevant.
        rank = i+1; // remember the rank of the first relevant document
     }
}, k);
const score = rank > 0 ? 1.0 / rank : 0.0;
setScore(score);