https://gitlab.dkrz.de/jsbach/jsbach/-/merge_requests/119



Changes in ICON-Land for the open source release.

- replace module headers with open source license text
- the file `LICENSE.md` contains the text of the license
- remove authors and revisions from module code including all doxygen keywords
- add `scripts/ci_scripts/check_license.sh` script to check for correct license headers ...
  it contains the license text that's expected and the test passes for the `src` directory

Merged-by: Reiner Schnur <reiner.schnur@mpimet.mpg.de>