treewide: standardize shell integration options

Standardize all 'programs.<PROGRAM>.enable<SHELL>Integration' options
with the following new functions:

- lib.hm.shell.mkBashIntegrationOption
- lib.hm.shell.mkFishIntegrationOption
- lib.hm.shell.mkIonIntegrationOption
- lib.hm.shell.mkNushellIntegrationOption
- lib.hm.shell.mkZshIntegrationOption

These functions should default to their corresponding global option:

- home.shell.enableBashIntegration
- home.shell.enableFishIntegration
- home.shell.enableIonIntegration
- home.shell.enableNushellIntegration
- home.shell.enableZshIntegration

All these global options default to the
'home.shell.enableShellIntegration' value.

This hierarchy standardizes the shell integration and increases end-user
flexibility.

BREAKING CHANGE: The following inconsistent default values change from
'false' to 'true':

- programs.zellij.enableBashIntegration
- programs.zellij.enableFishIntegration
- programs.zellij.enableZshIntegration

Link: https://github.com/nix-community/home-manager/pull/6358

Co-authored-by: Robert Helgesson <robert@rycee.net>

modules/lib/shell.nix

@@ -1,6 +1,22 @@
 { lib }:
 
-rec {
+let
+
+  mkShellIntegrationOption = name:
+    { config, baseName ? name, extraDescription ? "" }:
+    let attrName = "enable${baseName}Integration";
+    in lib.mkOption {
+      default = config.home.shell.${attrName};
+      defaultText = lib.literalMD "[](#opt-home.shell.${attrName})";
+      example = false;
+      description = "Whether to enable ${name} integration.${
+          lib.optionalString (extraDescription != "")
+          ("\n\n" + extraDescription)
+        }";
+      type = lib.types.bool;
+    };
+
+in rec {
   # Produces a Bourne shell like variable export statement.
   export = n: v: ''export ${n}="${toString v}"'';
 
@@ -8,4 +24,10 @@ rec {
   # assignment, this function produces a string containing an export
   # statement for each set entry.
   exportAll = vars: lib.concatStringsSep "\n" (lib.mapAttrsToList export vars);
+
+  mkBashIntegrationOption = mkShellIntegrationOption "Bash";
+  mkFishIntegrationOption = mkShellIntegrationOption "Fish";
+  mkIonIntegrationOption = mkShellIntegrationOption "Ion";
+  mkNushellIntegrationOption = mkShellIntegrationOption "Nushell";
+  mkZshIntegrationOption = mkShellIntegrationOption "Zsh";
 }