assistant/avante.nvim apply suggested changes

Change the options to use mkOption when applicable and apply changes to
descriptions
Change the building of the vimPlugin to use npin dependencies instead of
dependencies from nixpkgs

flake/packages.nix

@@ -28,6 +28,7 @@
             rev = pin.revision;
             sha256 = pin.hash;
           };
+          pins = self.pins;
         };
 
       inherit (docs.manual) htmlOpenTool;