Webcams: indicate who is sharing webcams in the interface

[prlanzarin]

Is your feature request related to a problem? Please describe.

There is currently no indicator in the UI that an user is sharing their webcam besides the video container itself.
The problem is more pronounced when pagination or a webcam restricting lock setting is enabled, which means a camera container might not be displayed for an user that is sharing their camera.

A similar scenario which is currently implemented is audio: microphone/listen only have indicators in the user list.

Describe the solution you'd like

When an user is sharing their webcam, that state should be reflected somewhere in the UI. Preferably in a place that is accessible no matter the state which the client ends up into.

Additional context

Example of similar situations are the microphone, listen only and presenter indicators in the user list's avatars.

Some design rationale here: #5035.