Make 'autofocus' on searchbar optional

[QuentinCG]

On some cases (if list is small), there is no point to do autofocus on the searchbar since the user would most likely want to click to the list directly and don't want the keyboard to appear.

Best way would be to make the autofocus by default "true" but editable in the constructors:

https://github.com/icemanbsi/searchable_dropdown/blob/799d871b6f82b121957ae63106156f556a7830f4/lib/searchable_dropdown.dart#L876

If needed I can do a pull request for this feature.

Without autofocus:

With autofocus:

[QuentinCG]

Seems to already have a pull request for that: https://github.com/icemanbsi/searchable_dropdown/pull/70

Do you think you'll integrate this pull request soon ?