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
By inline I meant applying <code>display: inline</code> to the descendents of the summary element (so my SCSS code block above should be added to src/base/details/_base.scss in that separate PR for the details/summary fixes).