Add visual regression testing for sample app

[szuperaz]

Motivation Setting up visual regressions through playwright seems fairly easy. A new theme would be the right moment to introduce such testing. Visual tests could also help us making sure that we don't break the old theme.

Proposed solution A clear and concise description of what you want to happen. We could use regression for the current theme and for the new theme as well

Acceptance Criteria A set of predefined requirements that must be met to mark a user story complete.