Nix: update and add documentation for nix subcommands (#9959)

* Nix: update and add documentation for nix subcommands

Updates the documentation on the new unstable Nix command & subcommands,
and adds a separate page for the Classic Nix commands.

---------

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>
Co-authored-by: axtloss <axtlos@getcryst.al>
Co-authored-by: CleanMachine1 <78213164+CleanMachine1@users.noreply.github.com>

pages/common/nix-store.md

@@ -0,0 +1,29 @@
+# nix-store
+
+> Manipulate or query the Nix store.
+> See also: `tldr nix3 store`.
+> More information: <https://nixos.org/manual/nix/stable/command-ref/nix-store.html>.
+
+- Collect garbage, such as removing unused paths:
+
+`nix-store --gc`
+
+- Hard-link identical files together to reduce space usage:
+
+`nix-store --optimise`
+
+- Delete a specific store path (must be unused):
+
+`nix-store --delete {{/nix/store/...}}`
+
+- Show all dependencies of a store path (package), in a tree format:
+
+`nix-store --query --tree {{/nix/store/...}}`
+
+- Calculate the total size of a certain store path with all the dependencies:
+
+`du -cLsh $(nix-store --query --references {{/nix/store/...}})`
+
+- Show all dependents of a particular store path:
+
+`nix-store --query --referrers {{/nix/store/...}}`