[MA-33]: Add aria-live to empty result messages

[SaurabhSharma-884]

Summary

• Added Aria-live to Empty Result message.
• Removed "application" role from the result region.

Steps to reproduce

MM-61607 :

• Navigate to the "Search result" modal section.
• Turn on the screen reader and navigate through the modal.
• Notice that the "No results for “message”....etc." element is not announced by the screen reader.

MM-61613 :

• Turn on the screen and navigate to the "Recent Mentions" button then select it.
• Navigate to the "No mentions yet,....etc." element.
• Notice that the screen reader does not announce the "No mentions yet,....etc." element.

Expected Behaviour

MM-61607 :
"No results for “message”....etc." element should be announced by the screen reader.

MM-61613 :
"No mentions yet,....etc." element should be announced by the screen reader.

Ticket Link

Fixes:

• https://mattermost.atlassian.net/browse/MM-61607
• https://mattermost.atlassian.net/browse/MM-61613

Screenshots

MM-61607 :

before	after

MM-61613 :

before	after

Release Note

NONE