[potd] Modernize configuration settings

Summary:
This patch replaces the ColumnLayout with Kirigami.FormLayout and make use of twinFormLayouts to link child layout with parent layout.

QQC1 comboboxes are retained due to a QQC2 bug with resizing the popup to delegate width.

Test Plan:

Reviewers: Plasma, VDG, ngraham

Reviewed By: VDG, ngraham

Subscribers: abetts, davidedmundson, plasma-devel

Tags: Plasma

Maniphest Tasks: T10586

Differential Revision: https://phabricator.kde.org/D20969