[Bug] Cerberus doesn't work with group chats and charters

[krivtsova-arina]

Description

1. Cerberus doesn't notify group chat members when a charter is fully signed by all members
2. Cerberus doesn't notify group chat members about charter violations, even when a member sends the message “cerberus trigger”.

Steps to reproduce

Steps to reproduce the behavior:

1. Create a group chat with 3 or more members (e.g. pictique chat uuid e64283e8-813e-49e0-a3bd-b0b9c3531357)
2. Create charter for this chat with an Automated Watchdog Policy block (e.g. uuid 75fbbefc-6c49-4b0d-a1a9-3f5041a0c244) and a runtime policy with an interval of 1 minute
3. Have all chat members sign the charter

Expected behavior

1. Cerberus joins the chat and notifies users that the charter has been signed
2. Cerberus processes the group chat for charter violations and sends notifications when violations occur