feat: accordion v-model

[davidnixon]

What did you do?

Added a v-model for accordion items open state

Why did you do it?

I have a design that calls for an "auto close" of sections such that when one section is opened, other sections close. There is not a way to implement this in current component.

How have you tested it?

With local story and in test app that implements the "auto close"

Were docs updated if needed?

• [x] Yes

[davidnixon]

FWIW, auto close code is included in the "docs" area of the storybook

// example auto close
// <cv-accordion @change="onAutoClose">
const open = ref({
  accItem1: false,
  accItem2: false,
  accItem3: false,
  accItem4: false,
});
function autoClose(ev) {
  if (ev.change.open) {
    for (let state in open.value) {
      if (state !== ev.change.id) open.value[state] = false;
    }
  }
}

[davidnixon]

@OlkaB could you review this one?