Make nuxeo-search-form results list in queue view usable with keyboard only

related to WCAG 2.1 level A criteria 2.1.1: Keyboard
https://www.w3.org/TR/WCAG21/#keyboard

Make nuxeo-search-form results list in queue view usable with keyboard only.

Location of the elements: List of buttons, under the "Search filters" section, on the left navigation section, in the "Search" sub-menu panel, on the left navigation.

Additional details: While navigating with the tab key, the above-mentioned buttons are not receiving the tab key focus. Due to tabindex='-1', those buttons are not receiving the tab key focus.

Steps to reproduce:
1. Click and expand the "Search" menu button.
Then enter Text" in the search edit field.
3. Then select any image from the list of image buttons in the main content.
4. Then the list of the above-mentioned buttons will display on the filter section on the left navigation section.

Recommendation to fix
RULE :
Functionality MUST be available using the keyboard, unless the functionality cannot be accomplished in any known way using a keyboard.

HOW TO FIX:
Fix this issue by ensuring the component can be used by the keyboard OR by providing a conformant alternate functionality method for the action

REFERENCE:
Deque University:https://dequeuniversity.com/class/input-methods2/keyboard-input/functionality

BACKGROUND:
Some people cannot use a mouse due to vision or motor disabilities. Content that can be operated with a mouse must also be made operable with a keyboard. When content is operable through a keyboard, it becomes operable by a variety of assistive technologies such as speech input software, sip-and-puff software, on-screen keyboards, scanning software, and alternate keyboards.