Modernize cmake

[LecrisUT]

The cmake project should be modernized in order to make the project accessible via FetchContent:

• Namespace the options and targets
• remove various variables that are available built-in, e.g. detecting the OS
• Add a NETCDF_INSTALL option with defaults if it's top_level or imported so that install is not called when imported
• export the variables in netCDFConfig.cmake at the new nd of the cmakelists.txt
• split the cmake file in subfolders
• deprecate old options (use if(DEFINED))
• change flags to be linked to a target, not global
• move nonessential flags (warnings etc.) to CI preset file
• use presets for the CI
• DO NOT set cache variables that can have name overlap with other projects
• separate into more targets and export them depending on options

Nitpicks:

• move all options near the top to make the options visible to importers
• move find_package/fetchcontent near the top as well
• move autotools definitions to an separate file
• move macros to a separate file and prefer using function

[K20shores]

@WardF you can assign this to me

[LecrisUT]

I can help with reviewing. Also I have a cmake-template with many of the points there, feel free to copy anything needed from there.