azure-cli: fix installing extensions externally

For those of us not using the new azure-cli-extensions mechanism to
manage extensions, it is not possible to install or update extensions
unless pip is on the PYTHONPATH.

This used to be the case by default, but a relatively recent change to
either Python packaging (likely
6c85fff302, as identified in other issues)
or construction of the PYTHONPATH in this package
aacf05daec removed it.

pkgs/tools/admin/azure-cli/default.nix

@@ -229,6 +229,10 @@ py.pkgs.toPythonApplication (py.pkgs.buildAzureCliPackage rec {
     wcwidth
     websocket-client
     xmltodict
+  ] ++ lib.optionals (!withImmutableConfig) [
+    # pip is required to install extensions locally, but it's not needed if
+    # we're using the default immutable configuration.
+    pip
   ];
 
   postInstall = ''