Aria properties for AutoComplete

[mattcfilbert]

I'm submitting a ...

[ ] bug report => Search github for a similar issue or PR before submitting
[X] feature request => Please check if request is not on the roadmap already https://github.com/primefaces/primeng/wiki/Roadmap
[ ] support request => Please do not submit support request here, instead see http://forum.primefaces.org/viewforum.php?f=35

Current behavior
Many input components (including autocomplete) can be made more accessible to the visually impaired by adding "aria-label" and "aria-required" attributes. The "required" attribute does a lot of what the "aria-required" attribute does, but the latter is still useful for user agents that do not yet support HTML5.

Proposed improvement
I am submitting a PR that adds "aria-label" and "aria-required" attributes to the autocomplete component.

What is the motivation / use case for changing the behavior?
This PR will improve PrimeNG's accessibility for visually impaired users who rely on screen readers.

NOTE: This issue is based on #6103, but focused on a specific component.