ui: generic-search - make results$ variable public in AbstractStarkSearchComponent

[SuperITMan]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[X] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/NationalBankBelgium/stark/blob/master/CONTRIBUTING.md#got-a-question-or-problem

Current behavior

It is not allowed to use results$ variable in template when extending AbstractStarkSearchComponent.

This variable contains the results of the search and can be used directly in template using | async pipe.

Expected behavior

This variable should be public.

What is the motivation / use case for changing the behavior?

Improve GenericSearch.

Environment

Angular version: 7.x
Stark version: 10.x & 12.x