[fenix] For https://github.com/mozilla-mobile/fenix/issues/9989: Add start & end margin to button.

app/src/main/res/layout/fragment_installed_add_on_details.xml

@@ -77,6 +77,7 @@
                 android:id="@+id/remove_add_on"
                 style="@style/DestructiveButton"
                 android:layout_below="@+id/permissions"
+                android:layout_marginHorizontal="16dp"
                 android:text="@string/mozac_feature_addons_remove" />
         </RelativeLayout>
     </ScrollView>