nixos/bash-completion: move options to programs.bash.completion, add package option, drop with lib

This allows to easily test bash-completion updates without triggering a mass rebuild locally.

nixos/modules/programs/bash/bash-completion.nix

@@ -1,16 +1,22 @@
 { config, lib, pkgs, ... }:
 
 let
-  enable = config.programs.bash.enableCompletion;
+  cfg = config.programs.bash;
 in
 {
-  options = {
-    programs.bash.enableCompletion = lib.mkEnableOption "Bash completion for all interactive bash shells" // {
+  options.programs.bash.completion = {
+    enable = lib.mkEnableOption "Bash completion for all interactive bash shells" // {
       default = true;
     };
+
+    package = lib.mkPackageOption pkgs "bash-completion" { };
   };
 
-  config = lib.mkIf enable {
+  imports = [
+    (lib.mkRenamedOptionModule [ "programs" "bash" "enableCompletion" ] [ "programs" "bash" "completion" "enable" ])
+  ];
+
+  config = lib.mkIf cfg.completion.enable {
     programs.bash.promptPluginInit = ''
       # Check whether we're running a version of Bash that has support for
       # programmable completion. If we do, enable all modules installed in
@@ -19,7 +25,7 @@ in
       # $XDG_DATA_DIRS/bash-completion/completions/
       # on demand, so they do not need to be sourced here.
       if shopt -q progcomp &>/dev/null; then
-        . "${pkgs.bash-completion}/etc/profile.d/bash_completion.sh"
+        . "${cfg.completion.package}/etc/profile.d/bash_completion.sh"
         nullglobStatus=$(shopt -p nullglob)
         shopt -s nullglob
         for p in $NIX_PROFILES; do