Tracking module system documentation

[hsjobeki]

This issue is intended to communicate remaining work specifically on the module system documentation.

This was mainly created out of #240531 and #390993 once merged this is some remaining work.

• More code examples
• Glossary that defines the often used terms (definitions module syntax ... )
• Clarify the target audience of module system documentation
• Place references between the tutorials, introduction and reference docs
• Link used terminology references to the glossary
• In code reference documentation for functions in:
  • modules.nix (i.e. evalModules )
  • options.nix (i.e. mkOption )
  • types.nix (i.e types.attrsOf )
• in code reference documention for everything that is not a function such as:
  • option-types (i.e types.int )
  • options ( i.e. unknownModule )
  • other object "classes" (i.e. definitions, declarations, option-type )
  • split out definition modifiers (mkIf mkForce, ... ) into a seperate file and automatically link them.