Adding `aria-describedby="elementId"` to tooltip plugin for better accessibility

Created by: bassettsj

Adding a bit of info to the item with aria-describedby to the tooltip/popover would help signal to Assistive Technology, like screen readers, that element getting targeted by the tooltip/popover that it is better described by this other DOM thing. This is illustrated on paypal/bootstrap-accessibility-plugin source line 32

Changes that would need to happen:

• Create an unique ID / or use for the target element on show
• Add an aria-describedby="elementId" on the element on show

We already have role="tooltip" 👍