Added dismissible alert plugin

This is the cleaned up version of https://github.com/wet-boew/wet-boew/pull/5932.
Please note the build will fail because of this issue: https://github.com/wet-boew/wet-boew/issues/5927
The pointer's size is dictated by the &lt;summary> element, so since there's no way to select a parent element in CSS, we'd have to do this in JavaScript, or, you'd apply the h3 class to &lt;summary> elements even if &lt;h3> is used as a children.