[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

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