Fix cognitive complexity in onUserInput method for tags input component

[samuil4]

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

Function onUserInput has a Cognitive Complexity of 8 (exceeds 5 allowed). Consider refactoring.

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