[IMP] web_editor: add correct spacing to add image from URL

When adding a media to the library using its external URL, the
confirmation icon (either error, warning, or success) will not be
spaced correctly, and will stick to the button on its right.

In this commit, we add a class to it which adds some padding on the
right.

task-2618494

Part-of: odoo/odoo#75730

addons/web_editor/static/src/xml/wysiwyg.xml

@@ -136,7 +136,7 @@
                     <button type="button" class="btn btn-secondary o_upload_media_url_button">
                         <t t-out="addText"/>
                     </button>
-                    <div class="ml-2">
+                    <div class="mx-2">
                         <span class="o_we_url_success text-success d-none fa fa-lg fa-check" title="The URL seems valid."/>
                         <span t-if="urlWarningTitle" class="o_we_url_warning text-warning d-none fa fa-lg fa-warning" t-att-title="urlWarningTitle"/>
                         <span class="o_we_url_error text-danger d-none fa fa-lg fa-times" title="The URL does not seem to work."/>