feat: show if the caller is busy on a call or available to receive calls

[almeydajuan]

I try to call a coworker that is online but the call is automatically rejected because this person is in another call.

I would like to know in advance if this person is in another call so I know that they are busy now. It would also be great to know who they are talking to, because this would be relevant to decide on joining them or not.

[konsalex]

Similar to #262 we will tackle this soon @almeydajuan 🙏