introduce frontend e2e test with cypress

[JannikStreek]

Unfortunately the frontend does not include many tests yet. I have already added chromium support to the development image, which can also be used by cypress, see https://docs.cypress.io/guides/guides/launching-browsers. We can either use a separate docker container for cypress or do it directly in the app container.

Test ideas:

• Visit the map, add a node with a name
• Visit the map, invoke share button
• Visit the map, add a node, increase font size
• Visit the map, add a node, decrease font size
• Visit the map, add a node and add a color
• Visit the map, add two nodes, cut one node an append it to the other
• Visit the map, import an existing map

https://angular.de/artikel/angular-cypress-typescript-e2e-testing/
https://www.tomray.dev/nestjs-unit-testing