Accordion - support for animation

[mcoker]

Core PR - patternfly/patternfly#7488

Same deal as <ExpandableSection>, we need to manage the hidden attribute to handle the show/hide of the element and an expanded class - #11807

[kmcfaul]

Pull in core-only approach once core PR merges & verify

May need an opt-in class to work around the first-load animation.