[FIX] web: add spacing in the DomainField

This commit adds some spacing between the text and the
button in the DomainField. Since the rewrite of the
field, the button was too close to the text that
preceded it. A minor margin have been added to the
button to avoid that.

Part-of: odoo/odoo#98387

addons/web/static/src/core/domain_selector/domain_selector_root_node.xml

@@ -11,7 +11,7 @@
                 <span>Match <strong>all records</strong></span>
                 <t t-if="!props.readonly">
                     <button
-                        class="btn btn-sm btn-primary o_domain_add_first_node_button"
+                        class="btn btn-sm btn-primary o_domain_add_first_node_button ms-1"
                         t-on-click="() => this.insertNode('leaf')"
                     >
                         <i class="fa fa-plus"/> Add filter