Accordion component doesn't work with screen reader

### Issue type

**I'm submitting a ...** (check one with "x")

* [ x] bug report
* [ ] feature request

### Issue description

**Current behavior:**

The accordion component does not announce correctly to the user with JAWS screen reader. I believe this is because JAWS does not detect a in the way the Nebular component is constructed.
**Expected behavior:**

The user should be notified if the accordion is expanded or collapsed and also instructed to press enter to activate the accordion. A correct example can be seen in the Bootstrap accordion.
**Steps to reproduce:**

Nebular accordion component example that does not announce correctly: https://akveo.github.io/nebular/docs/components/accordion/overview#nbaccordioncomponent

Bootstrap accordion component that does announce correctly:
https://getbootstrap.com/docs/5.0/components/accordion/

### Other information:
Using Nebular/theme 7.0.0