https://github.com/TheLartians/Ccache.cmake

No need to configure anything for ccache.

Closes #3123.

- The get the source code page now just references source code downloads
  as an archive.
- The GitLab and fork set up has been moved to the development workflows
  section.
- Added page on code review.

Does not interfere with CPM modules.

Thanks to Shuang for reporting.

Thanks for Alireza for reporting!

Will be available at e.g. https://doxygen.opengeosys.org/v6.3.3

Was not in use anymore.

- Use CMake presets
- Use in-source build-directories
- Removed some old IDE descriptions

- [web] Fixed release notes links
- [web] Added release procedure steps
- [ci] Fixed release creation order (before web page deployment)