Fix cognitive complexity in transformToLabelValuePairList method of typeahead component

[samuil4]

Function transformToLabelValuePairList has a Cognitive Complexity of 7 (exceeds 5 allowed)

https://codeclimate.com/github/SQ-UI/ng-sq-ui/projects/ng-form-elements/src/lib/typeahead/typeahead.component.ts/source?from_sha=e92389f3&to_sha=827d7606

This task has a bounty of 10 DEVs!