- adds missing header to files
- unify header
- add SPDX (https://spdx.dev/) identifier to header (first step for getting REUSE https://reuse.software/ compliant)
- reworked doxgen

- uses awesome doxygen theme: https://jothepro.github.io/doxygen-awesome-css/

Adresses: #183

- adds wiki pages to doxygen page
- adds doxygen modules for production code and tests

Remove old apps. Remove unused extensions. Add format checker extensions and flylint settings to workspace. Add multigpu build to all-apps.

Update ci jobs to new image 1.1. Add clangd file to satisfy clangd when indexing cuda files. For the same reason disable cuda response files for includes.

This fixes incorrect times in the logger output.

fix h2 distribution in MultiphaseNonReflectingOutflowBCAlgorithm; fix negative phi in MultiphaseVelocityBCAlgorithm and in MultiphaseSimpleVelocityBaseExternalPressureLBMKernel; add unit test für FineToCoarseVectorConnector; redesign nozzle simulation setup