Add filterInputAutoFocus property to Dropdown

[giovannispd]

[ ] bug report
[X ] feature request
[ ] support request

**Current behavior**
when dropdown (with filter) panel is opened, filter inputtext get focus

**Expected behavior**
the default behavior is ok on desktop, but in mobile the inputtext autofocus trigger the opening of
 the virtual keyboard that covers 50% of the view and components... is fine to have a prop to disable this autofocus.

* **React version:**
16.8.6

* **PrimeReact version:**
3.2.0

* **Browser:** 
All browsers
 
* **Language:** 
ES6/7

[mertsincan]

Name	Type	Default	Description
autoFocusFilterInput	boolean	true	When the panel is opened, it specifies that the filter input should focus automatically.