minor #19004 [AssetMapper] Change the structure of the importmap file (javiereguiluz)

This PR was merged into the 6.4 branch.

Discussion
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[AssetMapper] Change the structure of the importmap file

Fixes #18998.

Commits
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50bf3ec [AssetMapper] Change the structure of the imortmap file

Author: javiereguiluz

frontend/asset_mapper.rst

@@ -215,7 +215,7 @@ This adds the ``bootstrap`` package to your ``importmap.php`` file::
         // ...
 
         'bootstrap' => [
-            'url' => 'https://cdn.jsdelivr.net/npm/bootstrap@5.3.0/+esm',
+            'version' => '5.3.0',
         ],
     ];