core: differentiate inactive and forwarded group snd statuses (#4420)

* core: GroupSndStatus

* rfc

* encoding, db apis

* pending, forwarded statuses

* encoding

docs/rfcs/2024-07-09-group-snd-status.md

@@ -0,0 +1,47 @@
+# Group messages sending status
+
+## Problem
+
+Currently in UI chat item info:
+- There's no differentiation between sent messages and pending messages.
+- There's no differentiation between pending messages reasons (establishing connection or member inactivity).
+  - Since the former is usually not a case due to group forwarding, this can be ignored.
+- Messages to be forwarded by admin are not accounted.
+
+## Solution
+
+Differentiate new statuses for group sending in chat item info:
+- forwarded
+- inactive / pending
+
+Option 1 is to add statuses to CIStatus / ACIStatus types.
+
+Pros:
+- simple.
+
+Cons:
+- further muddies type of statuses for chat item with impossible states / different dimension, as it's not applicable directly to chat item but a technicality of group sending process.
+
+Option 2 is to create a new type, GroupSndStatus.
+
+```haskell
+data GroupSndStatus
+  = GSSNew
+  | GSSForwarded
+  | GSSInactive
+  | GSSSent
+  | GSSRcvd {msgRcptStatus :: MsgReceiptStatus}
+  | GSSError {agentError :: SndError}
+  | GSSWarning {agentError :: SndError}
+  | GSSInvalid {text :: Text}
+```
+
+Most statuses repeat CIStatus sending statuses, with addition of forwarded and inactive for group sending process.
+
+Pros:
+- separates concerns of chat item presentation from group sending process.
+- allows future extension without further muddying CIStatus types.
+
+Cons:
+- more work.
+- requires backwards compatible decoding with ACIStatus to read previous data from db.