[MA-16]: MM-61578:Ensure all interactive functionality is operable with the keyboard

[SaurabhSharma-884]

Summary

Fix the interactive controls that cannot be navigated to and operated with the keyboard alone in the Emoji picker modal. The "Add" on hover button in sidebar navigation

Steps to reproduce

• Press Tab repeatedly to navigate through the "Add" on hover elements in the page.
• If the control can be focused, attempt to interact with the control using Enter, Space, Up/Down Arrow, and any other applicable keystrokes.
• Notice that the control cannot be focused or that the control cannot be interacted with using the keyboard alone.

Expected Behaviour

• The button should be focusable and operable by the keyboard.
• Element can be triggered when using the SPACE bar or ENTER key.
• Element should have accessible name

Ticket Link

Fixes https://mattermost.atlassian.net/browse/MM-61578

Screenshots

Release Note