[dolphin/search] Search by (multiple) tags

Summary:
Adds a tag selector in the extended filters of the search box.
Selected tag or tags are added to the search query along with the other filters (type, date, rating).

FEATURE: 412564
CCBUG: 356062

Test Plan:
- Menu shows the user tags
- Picking any tag/s filters the search to that specific tag/s

{F7727909}

Reviewers: elvisangelaccio, ngraham, #dolphin, #vdg

Reviewed By: elvisangelaccio, ngraham, #dolphin, #vdg

Subscribers: kfm-devel

Tags: #dolphin

Maniphest Tasks: T9094

Differential Revision: https://phabricator.kde.org/D25130