Feature/75378 fix nested list header items

[sushmi21]

This PR fixes accessibility issues in list message

Success Criteria

• The header item in the list receives visible focus outline
• The button in the list header gets visible focus outline
• The focus border color of the header button is the contrasting color of the button background color
• The header button should not be nested inside the clickable header container div.
• When the button inside the clickable header is triggered, it should not bubble the click to the container div
• Action button of type 'web_url' should use 'a' tag instead of the 'button' tag with 'role=link'
• All type of action buttons should be keyboard accessible (If it is a link, then enter key press should trigger the link. If it is button, then space-bar or enter key should trigger it)
• Phone number button should receive visible focus border on keyboard focus
• The list should look and behave the same for mouse users.

How to test:

• Check the list item component in the demo page.
• Also, test it with webchat by configuring various different lists (with/ without header, with/ without buttons, without image, long subtitles etc) to see if nothing is broken.