Group chat/chat conference (only text and file transfers, no audio, no video)

Please enable group chat/chat conference https://git.jami.net/savoirfairelinux/ring-project/issues/711#note_15404.

Please enable it to work with a new Add button (aka Add participant?) which is soon to be released https://git.jami.net/savoirfairelinux/ring-project/issues/711#note_15406.

Thank you