Optimize PR checks

[mlqn]

Description

• Create a dockerfile for playwright tests to prevent installing it & browsers
• Add layer caching to the docker-compose command used during Playwright tests (https://stackoverflow.com/questions/61491484/how-to-cache-docker-compose-build-inside-github-action)
• Decouple frontend/backend
• The whole solution is built
• Exclude azure-devops-mock, testing/cypress and testing/playwright folders from Dockerfile (see: https://github.com/Altinn/altinn-studio/issues/13033)
• Check if more files/folders can be excluded from docker image, lint, typecheck, etc

Additional Information

No response

Tasks

No response

Acceptance Criterias

No response