Adapt requirement tag UI for large amount of items

In the requirements UI there is a bar to filter by tags.
That bar should be able to handle a large amount of tag.

Maybe the QToolBar used there can set to handle this.

Or put the bar into a QScrollArea.

Note add pagination support to QGitlabAPI lables (QGitlabClient::requestListofLabels - see QGitlabClient::requestIssues).