Custom content should be visible in quick search

Issue Summary

Apps that create custom content should have a way to make that content included in quick search.

For example, the app Community Questions for Confluence creates questions and answers that can be searched through regular search.

It has the custom content types

• ac:questions-answers-for-confluence:question
• ac:questions-answers-for-confluence:answer

However, 

1. If question was never viewed or viewed long time ago (majority of cases), then it is not searchable through Quick Search.
2. If the questions was viewed recently, it does not appear in Quick Search, but does appear in other searches, e.g Recently Viewed.

This is not the case for all Apps, as for some the content is only searchable through Advanced Search.

Notes

This was reported previously in https://jira.atlassian.com/browse/CONFCLOUD-60569 which has very little detail and only a reported fix version for Connect.