MessageBox Responsive Fix

[Akshun-01]

Make MessageBox Responsive and add arrow key iteration Feature to command Menu

Acceptance Criteria fulfillment

• [x] Make the message box responsive so that the mention and command menu can be opened without disturbing it.
• [x] Make the mention menu scrollable such that the current item is shown in the modal window
• [x] Add Arrow iteration Feature to the command menu, similar to the command menu.

Fixes #513

Video/Screenshots

https://github.com/RocketChat/EmbeddedChat/assets/93793691/e626e799-66c7-48f3-8659-f9d2a5c8ca5d

[Akshun-01]

This currently has a small bug, on pressing Enter while in the command menu, it sends / as a message. I am looking into it. Will fix this soon! ^^