add efSearch values (plural)

[nvzm123]

we need ability to run benchmarks with multiple values with respect to the efSearch parameter. note: the implementation for this should avoid rebuilding the indexes with respect to different efSearch values (when everything else held constant)

[nvzm123]

cc: @narangvivek10 @kshitizgupta21 @singhmanas1 @cjnolet

PR: #14