Motivation for this change

The current sections under Section II: Configuration of the NixOS Manual are as follows:

5. Configuration Syntax
    5.1. NixOS Configuration File
    5.2. Abstractions
    5.3. Modularity
    5.4. Syntax Summary
6. Package Management
    6.1. Declarative Package Management
        6.1.1. Customising Packages
        6.1.2. Adding Custom Packages
    6.2. Ad-Hoc Package Management
7. User Management
8. [...]

I propose changing the title of the "Configuration Syntax" section to "Options Management."

Although renaming the section involves some minor changes to its contents, this should make its contents much more easily discovered by new users of NixOS reading the Table of Contents.

In addition to better matching the contents of the section, it would allow for new sub-sections to be made in the future to further document the options management process, since the currently-named "Configuration Syntax" section is the best place in the manual to do so.

The reason for proposing this is #49899: better document nixos-options. If we rename this section, it would allow us to, in the future, add a subsection to specifically document accessing option values, among other things.

Most of the contents for a hypothetical "Accessing Option Values" section values is already written, found in [5.3 Modularity]. A dedicated section in the future would allow for further elaboration along with being more discoverable for readers who have not read the manual from start to finish (i.e. most, if not all, non-advanced users of NixOS, I assume).

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.

Since this is a non-minor change, I assume that I will likely have to make some changes based on feedback, assuming this is eligible for being merged at all. Because of this, I marked the title with [WIP]