Add Switch Camera Action for Call

- Adds a new "switch camera" action next to the camera toggle on mobile devices.
- Mobile devices now display 4 call actions outside the "More" dropdown instead of 3.
- It enables users to switch between front and rear cameras during an active call.
- RTC service now tracks the current camera facing mode.
- Video stream is reinitialized appropriately when the camera is switched.

mail: move discuss sidebar search bar to sticky top
discuss sidebar search feature was shown
in-between mailboxes (Inbox, history) and the 1st channel category.

For improved visibility of the feature, this is moved to the sticky
top part of the discuss sidebar.