Accessibility improvements with new options

[gnbm]

This PR is to provide some accessibility improvements with new options that will partially help with the reported issue #246

What was happening?

1. Axe scan:

2. Wave:

What are the new results?

1. Axe scan:

2. Wave:

What was done?

• Added new 'searchFormLabel' option. This option will the used to enhance accessibility when using the search functionality on the dropdowns. Default = 'Search'

• Added new 'ariaLabelText' option. This option will the used to enhance accessibility when focusing on the dropdown wrapper making it verbose. Default = 'Options list'

Still Missing

Regarding accessibility, there are still several issues pending that should be covered asap (as mentioned in the issue #246 ).
Such as:

• screen readers are not being able to read the options while navigating the list of options since the focus seems to stay on the search box (they spell "blank" or the text that is on the search box);
• screen readers are not being able to read the selected options;
• once on the list of options we cannot go back to the search box;
• we cannot reach the clear icons using the keyboard and they're not read by the screen readers;

[sa-si-dev]

@gnbm Thanks for your contribution.

I will check and merge it with the next release.