Inactive group members (simplified)

Problem

Groups traffic is higher than necessary due to sending messages to inactive group members.

When leaving or deleting group, batch db operations to optimize performance.
In agent - fix race where connection can be deleted while it has remaining pending messages.
- Current agent logic is to immediately delete connection if it has no rcv queues left.
- Simplest should be to make a smart version of deleteConn for this improvement, checking snd_messages table for remaining messages, and keep connection around in case there are.
- While this may improve delivery of group leave and delete messages, it may as well have undesirable side effects for other use cases, as any pending messages will be sent prior to deleting connection. For example, user sends several messages on bad network, decides to delete contact, messages are still delivered when user is on good network before deletion, even though this contradicts user's intent and messages hadn't left user's device at the time of deletion. Considering this race when it happens is identical to simply leaving groups by deleting app, or deleting user profile only locally, it may be a bad idea to affect regular contact deletion for this use case.

Mark members as inactive on QUOTA errors, reset as active on QCONT
- track group_members.inactive flag per group member
- on SMP.QUOTA error agent to notify client with ERR CONN QUOTA (new ConnectionErrorType QUOTA)
- on receiving QCONT agent to notify client (new event)
- apart from QCONT, reset on any message or receipt
Don't send to member if inactive
- don't send only content messages (x.msg.new, etc.) and always send messages altering group state?
- or don't send any messages?
Track number of skipped messages per member and first skipped message
- count group_members.skipped_msg_cnt
- only count messages of same types/criteria that are included into history
- track group_members.skipped_first_shared_msg_id (only content or including service messages?)
Send XGrpMsgSkipped before next message
- check skipped_msg_cnt > 0 and skipped_first_shared_msg_id is not null to only send once, reset after sending

XGrpMsgSkipped :: SharedMsgId -> Int64 -> ChatMsgEvent 'Json -- from, count