[ACA-19] show search libraries hint

[suzanadirla]

PR Checklist

Please check if your PR fulfills the following requirements:

- [x] The commit message follows our guidelines: https://github.com/Alfresco/alfresco-content-app/blob/master/CONTRIBUTING.md#commit
- [x] Tests for the changes have been added (for bug fixes / features)
- [ ] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application / Infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: https://issues.alfresco.com/jira/browse/ACA-1989

What is the new behavior?

fixes the Jira issue

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov-io]

Codecov Report

Merging #802 into development will increase coverage by 1.18%.
The diff coverage is 65.51%.

@@               Coverage Diff               @@
##           development     #802      +/-   ##
===============================================
+ Coverage        61.54%   62.72%   +1.18%     
===============================================
  Files              113      113              
  Lines             3799     3818      +19     
  Branches           620      622       +2     
===============================================
+ Hits              2338     2395      +57     
+ Misses            1352     1312      -40     
- Partials           109      111       +2

Impacted Files	Coverage Δ
...ries-results/search-libraries-results.component.ts	60% <0%> (-4.71%)	⬇️
src/app/directives/library-membership.directive.ts	82.14% <0%> (+55.35%)	⬆️
...-results/search-libraries-query-builder.service.ts	96.77% <100%> (+3.67%)	⬆️
src/app/services/content-management.service.ts	68.06% <100%> (+0.07%)	⬆️
...ch-input-control/search-input-control.component.ts	100% <100%> (+47.61%)	⬆️
...ents/search/search-input/search-input.component.ts	68.53% <86.66%> (+5.38%)	⬆️

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[DenysVuika]

Looks good, see comments for potential issue with memory leaks