[FEATURE] Add WithFieldName implementation to KNNQueryBuilder

[dzane17]

Is your feature request related to a problem?
We'd like to update relevant query builders with WithFieldName tag so that Query Insights can get field name information when present.

Parent issue: opensearch-project/query-insights#110

What solution would you like?
Add implements WithFieldName here:

k-NN/src/main/java/org/opensearch/knn/index/query/KNNQueryBuilder.java

Line 71 in 7991350

public class KNNQueryBuilder extends AbstractQueryBuilder<KNNQueryBuilder> {

Example:
https://github.com/opensearch-project/OpenSearch/blob/a609e634a348b76386fb11936bbe8c4b38ea72d0/server/src/main/java/org/opensearch/index/query/MatchQueryBuilder.java#L59

What alternatives have you considered?
A clear and concise description of any alternative solutions or features you've considered.

Do you have any additional context?
WithFieldName interface

[jmazanec15]

This should be fairly trivial as we already have this information in

k-NN/src/main/java/org/opensearch/knn/index/query/KNNQueryBuilder.java

Line 95 in 7991350

private final String fieldName;

.

@vamshin can you assign?